“From “Symmetry”: “How to do particle physics in a climate emergency”

From “Symmetry”

DOE’s Fermi National Accelerator Laboratory Wilson Hall.

DOE’s SLAC National Accelerator Laboratory campus with world’s first x-ray laser- the Linac Coherent Light Source (LCLS) unveiled in 2009.

2.7.23
Emily Driehaus

Scientists in the particle physics community are bringing environmental and climate issues to the table in discussions about future research.

CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC.

CERN CLIC Collider annotated

CERN CLIC annotated.

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan.

Chinese Circular Electron Positron Collider (CEPC) map. It would be housed in a hundred-kilometer- (62-mile-) round tunnel at one of three potential sites. The documents work under the assumption that the collider will be located near Qinhuangdao City around 200 miles east of Beijing.

Using a particle collider requires a lot of energy.

For one, colliders use superconducting magnets to steer the beams of particles they smash together. The fact that the magnets are superconducting means that once they are powered, they conduct electricity with perfect efficiency—without losing anything to resistance.

FNAL magnets such as this one, which is mounted on a test stand at Fermilab, for the High-Luminosity LHC. Credit: Reidar Hahn.

But to stay superconducting, these magnets must be cooled to temperatures chillier than outer space. That takes energy.

Refrigeration is also required to keep rooms full of servers from overheating as scientists collect and sort enormous amounts of data, and running those servers takes energy as well.

As scientists discuss the future of particle physics they are also considering the future of the planet. A white paper [below] produced as part of the Snowmass US high-energy physics community planning process details the ways that building and operating particle accelerators affect the environment—along with ways to mitigate those effects.

“Since we released our white paper on the topic, we’ve been getting quite a lot of interest in this,” says Véronique Boisvert, a professor at Royal Holloway, University of London, one of the authors. “At the Snowmass community meeting [in July 2022], it got quite a lot of acknowledgement, and I think the US community definitely feels that it’s an important topic.”

The paper lays out four areas in which physicists could make a difference: construction, high-power computing, greenhouse gases and travel.

“This has just become, literally, a much hotter topic in the world,” says Ken Bloom, a professor and chair of the physics department at the University of Nebraska, Lincoln, and another author of the white paper. “So to be able to contextualize this for particle physicists has been an interesting opportunity.”

Construction

Constructing a new physics facility, like the proposed Future Circular Collider, is a carbon-intensive process. According to the white paper Boisvert and Bloom worked on, excavation and pouring cement for the main tunnel for the FCC would release 237 kilotons of carbon dioxide, equivalent to the amount released during the redevelopment of a neighborhood in a major city.

Using greener, more sustainable building materials could mitigate some of these effects. For example, green cement, the manufacturing of which does not emit as much carbon as the manufacturing of traditional cement, is becoming a popular alternative.

Changing established processes and using new materials costs money. But Boisvert says she thinks these considerations will become routine for major construction projects in the future.

“These criteria that we’re used to optimizing in terms of the cost, in a sense, need to take into account the context of climate change,” she says. “If we want to minimize emissions, that means using more expensive processes or material, then that goes into the price tag. I think we’ll be forced to do that. I think in 2040, that will just be the kind of world we live in where we’re going to be constantly asked, ‘What are your carbon emissions and how are you minimizing them?’”

Computing

Powering an accelerator is not the only energy expense associated with high-energy physics. Collecting the huge amount of data particle accelerators produce requires high-performance computing.

Data from CERN is transmitted around the world using the Worldwide LHC Computing Grid, which has over 170 computing sites in 42 different countries. The carbon footprint of this activity varies greatly depending on the energy source for the electrical grid in a particular region.

“When we send our computing jobs, we don’t necessarily know exactly where they go because we use farms of computers all over the world,” Boisvert says. “Even two identical, competing jobs might end up using quite different amounts of carbon depending on which computer farm is being used and where it’s located.”

It’s difficult to completely mitigate carbon emissions if a region’s electrical grid runs on fossil fuels. But coordinated efforts to use the smallest amount of energy possible, like performing computing jobs at times of the day when there is less demand on the grid, could help to at least reduce some of these emissions.

European institutions in particular are looking for solutions to this sooner rather than later, Bloom says.

“There’s a lot of concerns about energy supplies,” he says. “The various large computing centers I interact with there, they’re all sort of preparing for possible cutbacks. They might force us to do our computing in a more power-efficient way.”

Greenhouse gases

The gases used in particle physics experiments can also contribute to the overall climate impact of an experiment.

Certain particle detectors use gases like hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and even sulfur hexafluoride (SF6), which the EPA classifies as the most potent greenhouse gas known. These gases have global warming potentials thousands of times higher than carbon dioxide and trap heat when released into the atmosphere, which contributes to rising global temperatures.

These gases are typically used in particle detectors and cooling systems. They’re good candidates for the job, since they are relatively cheap and their molecules can withstand heat and pressure. However, that tolerance is also what allows them to stick around in the Earth’s atmosphere.

“It’s a challenging problem because the gases really have been optimized for what you want to do, for the quality of the measurements you want to take,” Bloom says. “They’re also optimized for safety, you’ve got to pick nonflammable things that won’t explode.”

In accordance with the Kigali Amendment of the Montreal Protocol, which the US ratified in fall 2022, countries will phase out the use of HFCs by 2047. That will affect future detectors, but it would be difficult to replace the gases currently in use.

“Given where we are on the LHC right now with the experiments we’ve already built, we’re sort of committed to a lot of these gases,” Bloom says. “So you’re down to things like trying to fix leaks in the detectors and trying to do what you can to recuperate and recirculate gas.”

Bloom and Boisvert say now is the time to do R&D to figure out alternatives to these gases for the next generation of detectors.

“We’re used to thinking of a new facility in terms of the physics performance that it needs to achieve, and also in reducing the cost of it to make it easier for funding agencies to approve this project,” Boisvert says. “But I want to add to that list of criteria to take into account the sustainability of it.”

Travel

The white paper also addressed considerations related to travel.

“In some ways, we are in the lead on this, in that we already have these international collaborations that are highly distributed in terms of where the people are,” Bloom says. “We’re good at doing work without having to actually meet up.”

However, scientists still regularly fly to other cities and countries to attend scientific conferences, to spend time required by their collaborations taking shifts collecting data or working on their experiment’s detector, and to meet with other researchers on their experiments.

The rise of virtual events during the pandemic has made it even more possible to attend conferences on the other side of the world without taking a long-haul flight. The white paper suggests continuing to organize virtual and hybrid events. For in-person events, the paper recommends optimizing the location to minimize the distance participants must travel.

The authors propose creating regional hubs for international collaborations, following models such as the LHC Physics Center at Fermilab, a gathering place for US-based scientists working on the CMS experiment at the Large Hadron Collider.

However, implementing changes like these needs to happen in a way that does not isolate scientists from smaller countries or place undue burden on groups historically excluded from science, says Xavier Bertou, a physicist who worked on the regional strategy for high-energy physics, astrophysics and cosmology research in Latin America. A solution that may be convenient for researchers in North America or Europe may not be as convenient for researchers in South America or Africa.

“I am personally a bit worried that these discussions are actually very first-world centered,” Bertou said in an email. “I remember a survey where the first question was, ‘Would you agree to travel by train instead of plane?’ Which just makes no sense for us. There are no trains here, the only options are a 24-hour bus, or a 2-hour plane.”

Boisvert says she wants to find a solution to ensure all can participate fully, no matter where they are in the world. “I think we can’t just go back, we need to sort of keep moving forward,” Boisvert says. “We’ve been at the forefront, so we have to think, ‘Okay, what are the novel, creative ideas to make this happen?’”

All in this together

Climate and environmental impacts are coming up in discussions and planning processes for particle physics around the world.

Along with fellow London-based physicists Chamkaur Ghag, Francesco Spano and David Waters, Boisvert co-authored a white paper on climate impacts for the European Strategy Update. It was signed by almost 300 physicists working in Europe. In September 2022, CERN hosted a workshop about how to make particle physics more sustainable, from using different materials when building new facilities to making changes to the kind of food provided at catered events.

More recently, members of the Energy Working Group for the ongoing African Strategy for Fundamental and Applied Physics have been discussing the environmental impacts of different energy sources.

Discussions about sustainability have also been part of planning the proposed International Linear Collider in Japan. Known as the “Green ILC,” a group of researchers are working on ways to make the facility more environmentally friendly, such as using renewable energy to power the collider and recovering and reusing energy for local communities.

Bloom and Boisvert continue to spread the word about climate change in the context of particle physics. Both have given talks at universities and events, and they created a webpage where members of the particle physics community could register their support for sustainability initiatives in the field.

“Now is the time to start thinking about those criteria to make sure we don’t have to start from scratch,” Boisvert says. “We can put our minds to it. It sends a powerful message to other scientists, it sends a powerful message to government and society that we think, ‘Yes, this is what it means to live in a climate emergency. Whatever you do, you need to take into account the climate change context and what you are doing to minimize it.’”

white paper

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Symmetry is a joint Fermilab/SLAC publication.

From Science Magazine: “With to-do list checked off, U.S. physicists ask, ‘What’s next?’”

From Science Magazine

Oct. 2, 2020
Adrian Cho

SURF-Sanford Underground Research Facility, Lead, South Dakota, USA.

Physicists at the Stanford Underground Research Facility assemble the heart of the Lux-Zeplin dark matter detector, which will hold 7 tons of liquid xenon. Credit: Matthew Kapust/Sanford Underground Research Facility.

LZ xenon detector in the Surface Assembly Lab cleanroom at SURF

As U.S. particle physicists contemplate their future, they find themselves victims of their own surprising success. Seven years ago, the often fractious community hammered out its current research road map and rallied around it. Thanks to that unity—and generous budgets—the Department of Energy (DOE), the field’s main U.S. sponsor, has already started on almost every project on the list.

So next week, as U.S. particle physicists start to drum up new ideas for the next decade in a yearlong Snowmass process—named for the Colorado ski resort where such planning exercises once took place—they have no single big project to push for (or against). And in some subfields, the next steps seem far less obvious than they were 10 years ago. “We have to be much more open minded about what particle physics and fundamental physics are,” says Young-Kee Kim of the University of Chicago and chair of the American Physical Society’s division of particles and fields, which is sponsoring the planning exercise.

Ten years ago, the U.S. particle physics community was in disarray. The high-energy frontier had passed to CERN, the European particle physics laboratory near Geneva where, in 2012, the world’s biggest atom smasher, the Large Hadron Collider (LHC), blasted out the long-sought Higgs boson, the last piece in particle physicists’ standard model. Some physicists wanted the United States to build a huge experiment to fire elusive particles called neutrinos long distances through Earth to study how they “oscillate”—morph from one of their three types to another—as they zip along. Others wanted the United States to help push for the next big collider.

CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC.

China Circular Electron Positron Collider (CEPC) map. It would be housed in a hundred-kilometer- (62-mile-) round tunnel at one of three potential sites. The documents work under the assumption that the collider will be located near Qinhuangdao City around 200 miles east of Beijing.

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan.

Those tensions came to a head during the last Snowmass effort in 2013, and the subsequent deliberations of the particle physics project prioritization panel (P5), which wrote the road map. U.S. researchers agreed to build the neutrino experiment, but make it bigger and better by inviting international partners. They also decided to continue to participate fully in the LHC, and to pursue a variety of smaller projects at home. The next collider would have to wait. Most important, DOE officials warned, the squabbling and backstabbing had to stop. In fact, physicists recall, the 2013 process had an informal motto: “Bickering scientists get nothing.”

Physicists have just started to build the current plan’s centerpiece. The Long-Baseline Neutrino Facility (LBNF) at Fermi National Accelerator Laboratory (Fermilab) in Illinois will shoot the particles through 1300 kilometers of rock to the Deep Underground Neutrino Experiment (DUNE) in South Dakota, a detector filled with 40,000 tons of frigid liquid argon. LBNF/DUNE, which should come on in 2026, aims to be the definitive study of neutrino oscillations and whether they differ between neutrinos and antineutrinos, which could help explain how the universe generated more matter than antimatter.

FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA.

SURF DUNE LBNF Caverns at Sanford Lab.

“The angst in the neutrino community is a lot lower than it was last time around,” says Kate Scholberg, a neutrino physicist at Duke University. “The DUNE program will be going on at least into the 2030s.” However, researchers are already thinking of upgrades to the $2.6 billion experiment, she notes.

In other areas, the future looks less certain. The last time around, for example, scientists had a pretty clear path forward in their search for particles of dark matter—the so-far-unidentified stuff that appears to pervade the galaxies and bind them with its gravity. Researchers had built small underground detectors that searched for the signal of weakly interacting massive particles (WIMPs), the leading dark matter candidate, bumping into atomic nuclei. The obvious plan was to expand the detectors to the ton scale.

Now, two multiton WIMP detectors are under construction. But so far WIMPs haven’t shown up, and scaling up that technology further “is probably not going to work very well anymore,” says Marcelle Soares-Santos, a physicist at the University of Michigan, Ann Arbor. “So we need to think a little bit more out of the box.” Researchers are now contemplating a hunt for other types of dark matter particles, using new detectors that exploit quantum mechanical effects to achieve exquisite levels of sensitivity.

A perennial question for the field is what the next great particle collider will be. The obvious need is for one that fires electrons into positrons to crank out copious Higgs bosons and study their properties in detail, says Meenakshi Narain, a physicist at Brown University. But possible designs vary. Physicists in Japan are discussing such a Higgs factory in the form of a 30-kilometer-long linear electron-positron collider. Meanwhile, CERN has begun a study of an 80- to 100-kilometer circular collider. China has plans for a similar circular collider.

However, Vladimir Shiltsev, an accelerator physicist at Fermilab, says those aren’t the only potential options. “The real picture is much murkier.” Snowmass organizers have received at least 16 different proposals for colliders, including one that would smash together muons—heavier, unstable cousins of electrons—and another that would use photons. Snowmass participants should consider all options, Shiltsev says.

Joe Lykken, Fermilab’s deputy director for research, suggests physicists could even push for DOE to support a massive experiment that has nothing to do with particles: a next-generation detector of gravitational waves, ripples in spacetime set off when massive objects such as black holes spiral into each other. Their discovery in 2015 by the Laser Interferometer Gravitational-Wave Observatory (LIGO) opened a new window on the universe.

LIGO consists of two L-shaped optical instruments with arms 4 kilometers long in Louisiana and Washington; it was built by the National Science Foundation. The next generation of ground-based detectors could be 10 times as big, and might better fit DOE, which specializes in scientific megaprojects, Lykken says. “It starts to sound like the kind of thing that the DOE would be interested in and maybe required for,” he says.

During the coming year, Snowmass participants will air the more than 2000 ideas researchers have already proffered in two-page summaries. Then, a new P5 will formulate a new plan. Whatever ideas scientists come up with, to execute their new plan they’ll have to maintain the harmony that in recent years has made their planning process an exemplar to other fields. “Being unified is the new norm for us,” quips Jim Siegrist, DOE’s associate director for high energy physics. “So we have to continue to keep a lid on divisiveness and that’ll be a challenge.”

MIT /Caltech Advanced aLigo .

Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA.

Caltech/MIT Advanced aLigo detector installation Hanford, WA, USA.

VIRGO Gravitational Wave interferometer, near Pisa, Italy.

VIRGO Gravitational Wave interferometer, near Pisa, Italy.

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From U.S. Department of Energy Office of Science: “Future machines to explore new frontiers in particle physics”

From U.S. Department of Energy Office of Science

September 10, 2020

Jim Siegrist
Associate Director for High Energy Physics Office
U.S Department of Energy
Email: news@science.doe.gov

Particle physics is global. Addressing the full breadth of the field’s most urgent scientific questions requires expertise from around the world. The timeline for developing a world-class international facility to explore new frontiers in the subatomic world may take decades, but it is built from a multitude of milestones marking scientific and technical advances. The U.S. Department of Energy’s (DOE’s) Office of Science is working with partners around the globe to realise the next generation of particle physics facilities and enable future discoveries.

Studying the science of neutrinos

Today, the foundational groundwork is underway in the U.S. to host an international facility to study the science of neutrinos. These ghostly particles rarely interact with other forms of matter and change their flavour between three known types as they travel. To enable precision study of this puzzling behaviour, the Long-Baseline Neutrino Facility (LBNF) will produce the world’s most intense beam of neutrinos at DOE’s Fermi National Accelerator Laboratory (Fermilab), in Illinois, and send them 1,300 km through the earth to the Sanford Underground Research Facility in South Dakota.

SURF-Sanford Underground Research Facility, Lead, South Dakota, USA.

FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA.

A new superconducting particle accelerator at Fermilab, the Proton Improvement Plan II (PIP-II), will provide the high-intensity proton beam needed to create the neutrinos.

FNAL new superconducting accelerator Proton Improvement Plan II (PIP-II).

About 1,500 m below the surface of the Earth in South Dakota, the Deep Underground Neutrino Experiment (DUNE) will measure neutrinos as they arrive from Illinois as well as from natural sources, such as supernovas from our region of the Milky Way. An international collaboration of over 1,000 scientists from 33 countries is now working to develop and build the large-scale DUNE detector, using results from prototypes at the CERN Neutrino Platform to refine their design and affirm the technology.

International partnerships will play a crucial role in the successful realisation of this new international neutrino facility. The DOE Office of Science is working to strengthen existing collaborative partnerships in High Energy Physics and build new ones with global partners in order to bring together the necessary scientific talent and technical expertise. Formal agreements are currently in place with the European Organization for Nuclear Research (CERN) as well as the governments of India, Italy, and the United Kingdom, to contribute to different areas of this mega-scale neutrino endeavour.

Discussions to expand the partnerships are now underway with several other countries across Europe, Asia, and South America. In fact, through such cooperative partnerships, the contributions for PIP-II will make this facility the first accelerator project hosted in the U.S. with significant contributions from global partners.

Developing particle accelerator technology

The DOE Office of Science is also developing particle accelerator technology that will help enable future particle physics facilities around the world. DOE is supporting the development of a future “Higgs factory,” an electron-positron collider with international participation that could produce many Higgs bosons to enable precision studies that complement those at the Large Hadron Collider (LHC) at CERN.

To realise this vision, DOE supports the R&D of accelerator and detector technologies to enable Japan to move forward with the International Linear Collider (ILC).

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan.

Over the past year, DOE has also worked with the U.S. Department of State, The White House Office of Science & Technology Policy, and the National Security Council to make a concerted effort to support a Japanese initiative to move forward with the proposed ILC “Pre-Laboratory” phase of the project.

Our scientists are developing improvements to the superconducting technology that will increase accelerator cavity efficiency and reduce the cost of construction and subsequent operations.

FNAL A superconducting radiofrequency cavity responsible for accelerating particles at the new PIP-II accelerator.

In June, the CERN Council unanimously adopted the resolution updating the 2020 European Strategy for Particle Physics. As recently pointed out by the CERN Director-General, the strategy is visionary and ambitious while remaining realistic and prudent, emphasising many exciting future initiatives in particle physics that can be achieved in collaboration with global partners, including the DOE. As one of its high priorities, the European strategy reaffirms the successful completion of the high-luminosity upgrades of the LHC accelerator and the LHC experimental ATLAS and CMS detectors. To enable this next era of the LHC program, the DOE Office of Science is contributing key magnets and cavity components to the accelerator upgrade, including high-field niobium-tin-based superconducting magnets developed in the United States, as well as state-of-the-art detector elements for the ATLAS and CMS detector upgrades.

The future: New frontiers in particle physics

Looking to the farther future towards the next facility after the LHC, studies are underway for a Future Circular Collider (FCC), the next-generation complex that could reach particle collision energies over seven times that of the LHC. The development of such a facility is one of the key focal points of the 2020 update of the European strategy.

CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC.

Earlier this year, the DOE Office of Science partnered with CERN and national laboratories across Europe on a FCC Innovation Study as part of a European Commission Horizon 2020 Design Study initiative that would investigate the technical design for a 100 km circumference collider in the French-Swiss border, one that could also leverage the existing infrastructure at CERN. The study would enable scientists and engineers to optimise the particle collider design and plan investigations into a suitable civil engineering project while also allowing all global partners to integrate into the study’s network and user community.

Moreover, DOE and CERN have recently begun discussions to expand DOE’s cooperation into CERN’s proposed future collider and is looking forward to working with CERN and other global partners to envision the technology that could achieve a FCC. Overall, facilities such as the LHC, FCC and LBNF/DUNE/PIP-II across the frontiers of science and technology promise to enable our quest to explore and achieve groundbreaking discoveries.

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The mission of the Energy Department is to ensure America’s security and prosperity by addressing its energy, environmental and nuclear challenges through transformative science and technology solutions.

Science Programs Organization

The Office of Science manages its research portfolio through six program offices:

Advanced Scientific Computing Research
Basic Energy Sciences
Biological and Environmental Research
Fusion Energy Sciences
High Energy Physics
Nuclear Physics

The Science Programs organization also includes the following offices:

The Department of Energy’s Small Business Innovation Research and Small Business Technology Transfer Programs, which the Office of Science manages for the Department;
The Workforce Development for Teachers and Students program sponsors programs helping develop the next generation of scientists and engineers to support the DOE mission, administer programs, and conduct research; and
The Office of Project Assessment provides independent advice to the SC leadership regarding those activities essential to constructing and operating major research facilities.

From Brookhaven National Lab: “EIC R&D Yields Energy-saving Accelerator Innovations”

From Brookhaven National Lab

May 22, 2020
Karen McNulty Walsh
kmcnulty@bnl.gov

Vladimir Litvinenko, Thomas Roser, and Maria Chamizo-Llatas co-authored a paper describing a design for a possible future high-energy electron-positron collider in which an energy-recovery linac (ERL) recaptures and recycles both the particles and their energy.

As physicists developed plans for building an Electron-Ion Collider (EIC)—a next-generation nuclear physics facility to be built at the U.S. Department of Energy’s Brookhaven National Laboratory for nuclear physics research—they explored various options for accelerating the beams of electrons. One approach, developed by scientists at Brookhaven Lab and Stony Brook University, was to use an energy-recovery linear accelerator (ERL). The ERL would bring the electrons up to the energy needed to probe the inner structure of protons and atomic nuclei, and then decelerate the electrons and reuse most of their energy. The R&D to develop the innovative ERL may end up having a major impact in a different area of physics—high-energy particle physics, where the power needs make its energy-saving features particularly attractive.

“The power consumption of scientific instruments for particle physics experiments has steadily increased. To perform sustainable research, physicists are investigating ways to reduce that power consumption,” said Thomas Roser, head of Brookhaven Lab’s Collider-Accelerator Department, one of the scientists developing the ERL approach.

In a paper just published in the journal Physics Letters B, the authors describe how their innovations could tame the power requirements of an electron-positron (e-e+) collider—a next-generation high-energy particle physics research facility under discussion for possible future construction in Europe.

Colliding electrons and positrons

The particle physics community is in the early stages of planning for a possible future electron-positron collider, including discussing various designs and locations. In each of these setups, the facility would bring beams of negatively charged electrons (e-) into collisions with their positively charged antimatter counterparts, known as positrons (e+), to conduct precision studies of the properties of the Higgs boson. That’s the particle discovered at the Large Hadron Collider (LHC) in Europe in 2012 that is responsible for imparting mass to most fundamental particles in the Standard Model of particle physics.

“Learning more about the Higgs particle’s properties and interactions with other particles would help scientists unravel the mechanism behind this important foundation of how our universe works, and possibly uncover discrepancies that point to the existence of new particles or ‘new physics,’” said Brookhaven physicist Maria Chamizo-Llatas, a co-author on the paper.

Possible layout of an energy-recovery linac (ERL) electron-positron collider. Beams of electrons and positrons would each be accelerated in stages during four passes through two superconducting linacs, moving in opposite directions through the 100-kilometer-circumference ring after each acceleration pass. When the particles reach maximum energy (250 billion electron volts, or GeV, as shown on the inset graph) they would be brought into collision in one of the detectors (D1, D2). After collisions, smashed beams would be decelerated and cooled in low-energy (2 GeV) accelerator rings before repeating the acceleration-collision-deceleration process over and over again.

One of the possible designs is a “storage ring” 100-kilometers in circumference based at Europe’s CERN laboratory (home to the 27-kilometer circular LHC). Beams of electrons and positrons would circulate through the storage ring continuously and collide repeatedly to produce the desired data. An alternate design would consist of two large linear accelerators that produce straight-line, head-on smashups.

CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC

Power requirements for both of these setups are approaching hundreds of megawatts, Roser said—enough energy to power hundreds of thousands of homes.

In a storage ring, Roser noted, lots of energy gets lost as “synchrotron” radiation, a type of energy emitted by charged particles as they change direction moving around the circle (picture the way water sprays off a wet towel if you swirl it around above your head). “The higher the energy, the greater the synchrotron energy loss,” Roser said—and the greater the need to make up that loss by adding more energy to keep particles colliding.

In a collider using linear accelerators, no synchrotron radiation is emitted. But the used beams are discarded after a single pass through the accelerator. That means that the beam energy, and also all the beam particles, are lost. More energy is needed to accelerate fresh particle beams over and over.

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

The Brookhaven and Stony Brook physicists say their energy-recovery and beam-recycling ERL components could solve key problems of both alternate designs. As described in the new paper, it would cut the electric power needed to operate the 100-km ring-shaped facility under discussion in Europe to one third of what would be required without an ERL. And, by refreshing particle beams while recovering and reusing their energy, it would eliminate the need to dump and replace beams while still allowing single-pass collisions of tightly packed particles for maximum physics impact.

Reusing energy and recycling beams

The ERL would be made of superconducting radiofrequency (SRF) cavities, and act as “a perpetuum-mobile of some kind invented in 1960s by Maury Tigner at Cornell University,” explained Vladimir Litvinenko, a professor of physics at Stony Brook University with a joint appointment at Brookhaven Lab. “The main advantage of SRF cavities is that they consume very little energy while operating. They are perfectly suited to accelerate new particles by taking energy back from used particles,” he explained.

For an e-e+ collider, a multi-pass ERL would accelerate both sets of particles in stages to higher and higher energy each time they pass through the SRF linear accelerator. After each stage of acceleration, the particles would zip through a 100-kilometer ring-shaped tunnel back to the linear accelerator for the next stage of acceleration; electrons moving in one direction and positrons going the other way. Having the particles travel around such a large circular path helps to reduce the energy lost as synchrotron radiation.

“After colliding at the top energy, both electrons and positrons would give their energy back by passing through the same accelerator but in decelerating fashion,” Litvinenko said. “During deceleration, the particles’ energy is captured in the SRF cavities to be used for accelerating the next batch of particles.”

Importantly, not only the energy but also the particles themselves would be recycled after the collisions. Additional cooling components would ensure that the particles stay tightly packed to keep collision rates high but power requirements relatively low.

“By taming the need for power and reusing particles in an e-e+ collider, our design would allow scientists to perform cutting-edge research in a sustainable way,” Roser said.

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Brookhaven campus

BNL Center for Functional Nanomaterials

BNL NSLS-II

BNL NSLS II

BNL RHIC Campus

BNL/RHIC Star Detector

BNL Phenix Detector

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

From CERN Courier: “European strategy [for HEP] enters next phase”

From CERN Courier

2 October 2019

Matthew Chalmers, editor

European strategy enters next phase

Physicists in Europe have published a 250-page “briefing book” to help map out the next major paths in fundamental exploration. Compiled by an expert physics-preparatory group set up by the CERN Council, the document is the result of an intense effort to capture the status and prospects for experiment, theory, accelerators, computing and other vital machinery of high-energy physics.

Last year, the European Strategy Group (ESG) — which includes scientific delegates from CERN’s member and associate-member states, directors and representatives of major European laboratories and organisations and invitees from outside Europe — was tasked with formulating the next update of the European strategy for particle physics. Following a call for input in September 2018, which attracted 160 submissions, an open symposium was held in Granada, Spain, on 13-16 May at which more than 600 delegates discussed the potential merits and challenges of the proposed research programmes. The ESG briefing book distills input from the working groups and the Granada symposium to provide an objective scientific summary.

“This document is the result of months of work by hundreds of people, and every effort has been made to objectively analyse the submitted inputs,” says ESG chair Halina Abramowicz of Tel Aviv University. “It does not take a position on the strategy process itself, or on individual projects, but rather is intended to represent the forward thinking of the community and be the main input to the drafting session in Germany in January.”

Collider considerations

An important element of the European strategy update is to consider which major collider should follow the LHC. The Granada symposium revealed there is clear support for an electron–positron collider to study the Higgs boson in greater detail, but four possible options at different stages of maturity exist: an International Linear Collider (ILC) in Japan, a Compact Linear Collider (CLIC) or Future Circular Collider (FCC-ee) at CERN, and a Circular Electron Positron Collider (CEPC) in China. The briefing book states that, in a global context, CLIC and FCC-ee are competing with the ILC and with CEPC. As Higgs factories, however, the report finds all four to have similar reach, albeit with different time schedules and with differing potentials for the study of physics topics at other energies.

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

CLIC Collider annotated

CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC

China Circular Electron Positron Collider (CEPC) map

Also considered in depth are design studies in Europe for colliders that push the energy frontier, including a 3 TeV CLIC and a 100 TeV circular hadron collider (FCC-hh). The briefing book details the estimated timescales to develop some of these technologies, observing that the development of 16 T dipole magnets for FCC-hh will take a comparable time (about 20 years) to that projected for novel acceleration technologies such as plasma-wakefield techniques to reach conceptual designs.

“The Granada symposium and the briefing book mention the urgent need for intensifying accelerator R&D, including that for muon colliders,” says Lenny Rivkin of Paul Scherrer Institut, who was co-convener of the chapter on accelerator science and technology. “Another important aspect of the strategy update is to recognize the potential impact of the development of accelerator and associated technology on the progress in other branches of science, such as astroparticle physics, cosmology and nuclear physics.”

The bulk of the briefing book details the current physics landscape and prospects for progress, with chapters devoted to electroweak physics, strong interactions, flavour physics, neutrinos, cosmic messengers, physics beyond the Standard Model, and dark-sector exploration. A preceding chapter about theory emphasises the importance of keeping theoretical research in fundamental physics “free and diverse” and “not only limited to the goals of ongoing experimental projects”. It points to historical success stories such as Peter Higgs’ celebrated 1964 paper, which had the purely theoretical aim to show that Gilbert’s theorem is invalid for gauge theories at a time when applications to electroweak interactions were well beyond the horizon.

“While an amazing amount of progress has been made in the past seven years since the Higgs boson discovery, our knowledge of the couplings of the Higgs-boson to the W and Z and to third-generation charged fermions is quite imprecise, and the couplings of the Higgs boson to the other charged fermions and to itself are unmeasured,” says Beate Heinemann of DESY, who co-convened the report’s electroweak chapter. “The imperative to study this unique particle further derives from its special properties and the special role it might play in resolving some of the current puzzles of the universe, for example dark matter, the matter-antimatter asymmetry or the hierarchy problem.”

Readers are reminded that the discovery of neutrino oscillations constitutes a “laboratory” proof of physics beyond the Standard Model. The briefing book also notes the significant role played by Europe, via CERN, in neutrino-experiment R&D since the last strategy update concluded in 2013. Flavour physics too should remain at the forefront of the European strategy, it argues, noting that the search for flavour and CP violation in the quark and lepton sectors at different energy frontiers “has a great potential to lead to new physics at moderate cost”. An independent determination of the proton structure is needed if present and future hadron colliders are to be turned into precision machines, reports the chapter on strong interactions, and a diverse global programme based on fixed-target experiments as well as dedicated electron-proton colliders is in place.

Europe also has the opportunity to play a leading role in the searches for dark matter “by fully exploiting the opportunities offered by the CERN facilities, such as the SPS, the potential Beam Dump Facility, and the LHC itself, and by supporting the programme of searches for axions to be hosted at other European institutions”. The briefing book notes the strong complementarity between accelerator and astrophysical searches for dark matter, and the demand for deeper technology sharing between particle and astroparticle physics.

Scientific diversity

The diversity of the experimental physics programme is a strong feature of the strategy update. The briefing book lists outstanding puzzles that did not change in the post-Run 2 LHC era – such as the origin of electroweak symmetry breaking, the nature of the Higgs boson, the pattern of quark and lepton masses and the neutrino’s nature – that can also be investigated by smaller scale experiments at lower energies, as explored by CERN’s dedicated Physics Beyond Colliders initiative.

Finally, in addressing the vital roles of detector & accelerator development, computing and instrumentation, the report acknowledges both the growing importance of energy efficiency and the risks posed by “the limited amount of success in attracting, developing and retaining instrumentation and computing experts”, urging that such activities be recognized correctly as fundamental research activities. The strong support in computing and infrastructure is also key to the success of the high-luminosity LHC which, the report states, will see “a very dynamic programme occupying a large fraction of the community” during the next two decades – including a determination of the couplings between the Higgs boson and Standard Model particles “at the percent level”.

Following a drafting session to take place in Bad Honnef, Germany, on 20-24 January, the ESG is due to submit its recommendations for the approval of the CERN Council in May 2020 in Budapest, Hungary.

“Now comes the most challenging part of the strategy update process: how to turn the exciting and well-motivated scientific proposals of the community into a viable and coherent strategy which will ensure progress and a bright future for particle physics in Europe,” says Abramowicz. “Its importance cannot be overestimated, coming at a time when the field faces several crossroads and decisions about how best to maintain progress in fundamental exploration, potentially for generations to come.”

See the full article here .

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THE FOUR MAJOR PROJECT COLLABORATIONS

ATLAS

CERN/ATLAS detector

ALICE

CERN/ALICE Detector

CMS

LHCb

LHC

CERN map

From Ethan Siegel: “Forget About Electrons And Protons; The Unstable Muon Could Be The Future Of Particle Physics”

From Ethan Siegel
Aug 29, 2019

The particle tracks emanating from a high energy collision at the LHC in 2014 show the creation of many new particles. It’s only because of the high-energy nature of this collision that new masses can be created. (WIKIMEDIA COMMONS USER PCHARITO)

Electron-positron or proton-proton colliders are all the rage. But the unstable muon might be the key to unlocking the next frontier.

If you want to probe the frontiers of fundamental physics, you have to collide particles at very high energies: with enough energy that you can create the unstable particles and states that don’t exist in our everyday, low-energy Universe. So long as you obey the Universe’s conservation laws and have enough free energy at your disposal, you can create any massive particle (and/or its antiparticle) from that energy via Einstein’s E = mc².

Traditionally, there have been two strategies to do this.

Collide electrons moving in one direction with positrons moving in the opposite direction, tuning your beams to whatever energy corresponds to the mass of particles you wish to produce.
Collide protons in one direction with either other protons or anti-protons in the other, reaching higher energies but creating a much messier, less controllable signal to extract.

One Nobel Laureate, Carlo Rubbia, has called for physicists to build something entirely novel: a muon collider.

Carlo Rubbia at the 62nd Lindau Nobel Laureate Meeting on July 4, 2012. Markus Pössel (user name: Mapos)

It’s ambitious and presently impractical, but it just might be the future of particle physics.

The particles and antiparticles of the Standard Model have now all been directly detected, with the last holdout, the Higgs Boson, falling at the LHC earlier this decade.

Standard Model of Particle Physics

CERN CMS Higgs Event

CERN ATLAS Higgs Event

All of these particles can be created at LHC energies, and the masses of the particles lead to fundamental constants that are absolutely necessary to describe them fully. These particles can be well-described by the physics of the quantum field theories underlying the Standard Model, but they do not describe everything, like dark matter. (E. SIEGEL / BEYOND THE GALAXY)

Above, you can see the particles and antiparticles of the Standard Model, which have now all been discovered. The Large Hadron Collider (LHC) at CERN discovered the Higgs boson, the long-sought-after last holdout, earlier this decade.

While there’s still much science left to be done at the LHC — it’s only taken 2% of all the data it will acquire by the end of the 2030s — particle physicists are already looking ahead to the next generation of future colliders.

A hypothetical new accelerator, either a long linear one or one inhabiting a large tunnel beneath the Earth, could dwarf the sensitivity to new particles that prior and current colliders can achieve. Even at that, there’s no guarantee we’ll find anything new, but we’re certain to find nothing new if we fail to try. ILC collaboration

All of the plans put forth involve scaled-up version of existing technologies that have been used in past and/or current accelerators. We know how to accelerate electrons, positrons, and protons in a straight line. We know how to bend them into a circle, and maximize both the energy of the collisions and the number of particles colliding per second. Larger, more energetic versions of existing technologies are the simplest approach.

FNAL/Tevatron map

CERN map

Future Circular Collider (FCC) Larger LHC

CERN FCC Future Circular Collider map

CERN Future Circular Collider

The scale of the proposed Future Circular Collider (FCC), compared with the LHC presently at CERN and the Tevatron, formerly operational at Fermilab. The Future Circular Collider is perhaps the most ambitious proposal for a next-generation collider to date, including both lepton and proton options as various phases of its proposed scientific programme. (PCHARITO / WIKIMEDIA COMMONS)

Of course, there are both benefits and drawbacks to each method we could use. You can build a linear collider, but the energy you can reach is going to be limited by how powerfully you can impart energy to these particles per-unit-distance as well as how long you build your accelerator. The drawback is that, without a continuous injection of circulating particles, linear colliders have lower collision rates and take longer amounts of time to collect the same amount of data.

The other main style of collider is the style currently used at CERN: circular colliders. Instead of only getting one continuous shot to accelerate your particles before giving them the opportunity to collide, you speed them up while bending them in a circle, adding more and more particles to each clockwise and counterclockwise beam with every revolution. You set up your detectors at designated collision points, and measure what comes out.

A candidate Higgs event in the ATLAS detector. Note how even with the clear signatures and transverse tracks, there is a shower of other particles; this is due to the fact that protons are composite particles. This is only the case because the Higgs gives mass to the fundamental constituents that compose these particles. At high enough energies, the currently most-fundamental particles known may yet split apart themselves. (THE ATLAS COLLABORATION / CERN)

CERN ATLAS Image Claudia Marcelloni

This is the preferred method, so long as your tunnel is long enough and your magnets are strong enough, for both electron/positron and proton/proton colliders. Compared to linear colliders, with a circular collider, you get

greater numbers of particles inside the beam at any one time,
second and third and thousandth chances for particles that missed one another on the prior pass through,
and much greater collision rates overall, particularly for lower-energy heavy particles like the Z-boson.

In general, electron/positron colliders are better for precision studies of known particles, while proton/proton colliders are better for probing the energy frontier.

A four-muon candidate event in the ATLAS detector at the Large Hadron Collider. The muon/anti-muon tracks are highlighted in red, as the long-lived muons travel farther than any other unstable particle. The energies achieved by the LHC are sufficient for creating Higgs bosons; previous electron-positron colliders could not achieve the necessary energies. (ATLAS COLLABORATION/CERN)

In fact, if you compare the LHC — which collides protons with protons — with the previous collider in the same tunnel (LEP, which collided electrons with positrons), you’d find something that surprises most people: the particles inside LEP went much, much faster than the ones inside the LHC!

CERN LEP Collider

CERN LEP Collider

Everything in this Universe is limited by the speed of light in a vacuum: 299,792,458 m/s. It’s impossible to accelerate any massive particle to that speed, much less past it. At the LHC, particles get accelerated up to extremely high energies of 7 TeV per particle. Considering that a proton’s rest energy is only 938 MeV (or 0.000938 TeV), it’s easy to see how it reaches a speed of 299,792,455 m/s.

But the electrons and positrons at LEP went even faster: 299,792,457.9964 m/s. Yet despite these enormous speeds, they only reached energies of ~110 GeV, or 1.6% the energies achieved at the LHC.

Let’s understand how colliding particles create new ones. First, the energy available for creating new particles — the “E” in E = mc² — comes from the center-of-mass energy of the two colliding particles. In a proton-proton collision, it’s the internal structures that collide: quarks and gluons. The energy of each proton is divided up among many constituent particles, and these particles zip around inside the proton as well. When two of them collide, the energy available for creating new particles might still be large (up to 2 or 3 TeV), but isn’t the full-on 14 TeV.

But the electron-positron idea is a lot cleaner: they’re not composite particles, and they don’t have internal structure or energy divided among constituents. Accelerate an electron and positron to the same speed in opposite directions, and 100% of that energy goes into creating new particles. But it won’t be anywhere near 14 TeV.

A number of the various lepton colliders, with their luminosity (a measure of the collision rate and the number of detections one can make) as a function of center-of-mass collision energy. Note that the red line, which is a circular collider option, offers many more collisions than the linear version, but gets less superior as energy increases. Beyond about 380 GeV, circular colliders cannot achieve those energies, and a linear collider like CLIC is the far superior option. (GRANADA STRATEGY MEETING SUMMARY SLIDES / LUCIE LINSSEN (PRIVATE COMMUNICATION))

Even though electrons and positrons go much faster than protons do, the total amount of energy a particle possesses is determined by its speed and also its original mass. Even though the electrons and positrons are much closer to the speed of light, it takes nearly 2,000 of them to make up as much rest mass as a proton. They have a greater speed but a much lower rest mass, and hence, a lower energy overall.

There’s a good physics reasons why, even with the same radius ring and the same strong magnetic fields to bend them into a circle, electrons won’t reach the same energy as protons: synchrotron radiation. When you accelerate a charged particle with a magnetic field, it gives off radiation, which means it carries energy away.

Relativistic electrons and positrons can be accelerated to very high speeds, but will emit synchrotron radiation (blue) at high enough energies, preventing them from moving faster. This synchrotron radiation is the relativistic analog of the radiation predicted by Rutherford so many years ago, and has a gravitational analogy if you replace the electromagnetic fields and charges with gravitational ones. (CHUNG-LI DONG, JINGHUA GUO, YANG-YUAN CHEN, AND CHANG CHING-LIN, ‘SOFT-X-RAY SPECTROSCOPY PROBES NANOMATERIAL-BASED DEVICES’)

The amount of energy radiated away is dependent on the field strength (squared), the energy of the particle (squared), but also on the inherent charge-to-mass ratio of the particle (to the fourth power). Since electrons and positrons have the same charge as the proton, but just 1/1836th of a proton’s mass, that synchrotron radiation is the limiting factor for electron-positron systems in a circular collider. You’d need a circular collider 100 km around just to be able to create a pair of top-antitop quarks in a next-generation particle accelerator using electrons and positrons.

This is where the big idea of using muons comes in. Muons (and anti-muons) are the cousins of electrons (and positrons), being:

fundamental (and not composite) particles,
being 206 times as massive as an electron (with a much smaller charge-to-mass ratio and much less synchrotron radiation),
and also, unlike electrons or positrons, being fundamentally unstable.

That last difference is the present dealbreaker: muons have a mean lifetime of just 2.2 microseconds before decaying away.

An earlier design plan (now defunct) for a full-scale muon-antimuon collider at Fermilab, the source of the world’s second-most powerful particle accelerator behind the LHC at CERN. (FERMILAB)

In the future, however, we might be able to work around that anyway. You see, Einstein’s special relativity tells us that as particles move closer and closer to the speed of light, time dilates for that particle in the observer’s reference frame. In other words, if we make this muon move fast enough, we can dramatically increase the time it lives before decaying; this is the same physics behind why cosmic ray muons pass through us all the time!

If we could accelerate a muon up to the same 6.5 TeV in energy that LHC protons achieved during their prior data-taking run, that muon would live for 135,000 microseconds instead of 2.2 microseconds: enough time to circle the LHC some 1,500 times before decaying away. If you could collide a muon/anti-muon pair at those speeds, you’d have 100% of that energy — all 13 TeV of it — available for particle creation.

The prototype MICE 201-megahertz RF module, with the copper cavity mounted, is shown during assembly at Fermilab. This apparatus could focus and collimate a muon beam, enabling the muons to be accelerated and survive for much longer than 2.2 microseconds. (Y. TORUN / IIT / FERMILAB TODAY)

Humanity can always choose to build a bigger ring or invest in producing stronger-field magnets; those are easy ways to go to higher energies in particle physics. But there’s no cure for synchrotron radiation with electrons and positrons; you’d have to use heavier particles instead. There’s no cure for energy being distributed among multiple constituent particles inside a proton; you’d have to use fundamental particles instead.

The muon is the one particle that could solve both of these issues. The only drawback is that they’re unstable, and difficult to keep alive for a long time. However, they’re easy to make: smash a proton beam into a piece of acrylic and you’ll produce pions, which will decay into both muons and anti-muons. Accelerate those muons to high energy and collimate them into beams, and you can put them in a circular collider.

While many unstable particles, both fundamental and composite, can be produced in particle physics, only protons, neutrons (bound in nuclei) and the electron are stable, along with their antimatter counterparts and the photon. Everything else is short-lived, but if muons can be kept at high enough speeds, they might live long enough to forge a next-generation particle collider out of. (CONTEMPORARY PHYSICS EDUCATION PROJECT (CPEP), U.S. DEPARTMENT OF ENERGY / NSF / LBNL)

The MICE collaboration — which stands for Muon Ionization Cooling Experiment — continues to push this technology to new heights, and may make a muon collider a real possibility for the future. The goal is to reveal whatever secrets nature might have waiting in store for us, and these are secrets we cannot predict. As Carlo Rubbia himself said,

“…these fundamental choices are coming from nature, not from individuals. Theorists can do what they like, but nature is the one deciding in the end….”

See the full article here .

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“Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

From Ethan Siegel: “Does Particle Physics Have A Future On Earth?”

From Ethan Siegel
Jun 11. 2019

The inside of the LHC, where protons pass each other at 299,792,455 m/s, just 3 m/s shy of the speed of light. As powerful as the LHC is, the cancelled SSC could have been three times as powerful, and may have revealed secrets of nature that are inaccessible at the LHC. (CERN)

If we don’t push the frontiers of physics, we’ll never learn what lies beyond our current understanding.

At a fundamental level, what is our Universe made of? This question has driven physics forward for centuries. Even with all the advances we’ve made, we still don’t know it all. While the Large Hadron Collider discovered the Higgs boson and completed the Standard Model earlier this decade, the full suite of the particles we know of only make up 5% of the total energy in the Universe.

CERN CMS Higgs Event

CERN ATLAS Higgs Event

Standard Model of Particle Physics

We don’t know what dark matter is, but the indirect evidence for it is overwhelming.

Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

Fritz Zwicky from http:// palomarskies.blogspot.com

Coma cluster via NASA/ESA Hubble

Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)

Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)

Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

Same deal with dark energy.

Dark Energy Survey

Dark Energy Camera [DECam], built at FNAL

NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

Timeline of the Inflationary Universe WMAP

The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

DES is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

Or questions like why the fundamental particles have the masses they do, or why neutrinos aren’t massless, or why our Universe is made of matter and not antimatter. Our current tools and searches have not answered these great existential puzzles of modern physics. Particle physics now faces an incredible dilemma: try harder, or give up.

The Standard Model of particle physics accounts for three of the four forces (excepting gravity), the full suite of discovered particles, and all of their interactions. Whether there are additional particles and/or interactions that are discoverable with colliders we can build on Earth is a debatable subject, but one we’ll only know the answer to if we explore past the known energy frontier. (CONTEMPORARY PHYSICS EDUCATION PROJECT / DOE / NSF / LBNL)

The particles and interactions that we know of are all governed by the Standard Model of particle physics, plus gravity, dark matter, and dark energy. In particle physics experiments, however, it’s the Standard Model alone that matters. The six quarks, charged leptons and neutrinos, gluons, photon, gauge bosons and Higgs boson are all that it predicts, and each particle has been not only discovered, but their properties have been measured.

As a result, the Standard Model is perhaps a victim of its own success. The masses, spins, lifetimes, interaction strengths, and decay ratios of every particle and antiparticle have all been measured, and they agree with the Standard Model’s predictions at every turn. There are enormous puzzles about our Universe, and particle physics has given us no experimental indications of where or how they might be solved.

The particles and antiparticles of the Standard Model have now all been directly detected, with the last holdout, the Higgs Boson, falling at the LHC earlier this decade. All of these particles can be created at LHC energies, and the masses of the particles lead to fundamental constants that are absolutely necessary to describe them fully. These particles can be well-described by the physics of the quantum field theories underlying the Standard Model, but they do not describe everything, like dark matter. (E. SIEGEL / BEYOND THE GALAXY)

It might be tempting, therefore, to presume that building a superior particle collider would be a fruitless endeavor. Indeed, this could be the case. The Standard Model of particle physics has explicit predictions for the couplings that occur between particles. While there are a number of parameters that remain poorly determined at present, it’s conceivable that there are no new particles that a next-generation collider could reveal.

The heaviest Standard Model particle is the top quark, which takes roughly ~180 GeV of energy to create. While the Large Hadron Collider can reach energies of 14 TeV (about 80 times the energy needed to create a top quark), there might not be any new particles present to find unless we reach energies in excess of 1,000,000 times as great. This is the great fear of many: the possible existence of a so-called “energy desert” extending for many orders of magnitude.

There is certainly new physics beyond the Standard Model, but it might not show up until energies far, far greater than what a terrestrial collider could ever reach. Still, whether this scenario is true or not, the only way we’ll know is to look. In the meantime, properties of the known particles can be better explored with a future collider than any other tool. The LHC has failed to reveal, thus far, anything beyond the known particles of the Standard Model. (UNIVERSE-REVIEW.CA)

But it’s also possible that there is new physics present at a modest scale beyond where we’ve presently probed. There are many theoretical extensions to the Standard Model that are quite generic, where deviations from the Standard Model’s predictions can be detected by a next-generation collider.

If we want to know what the truth about our Universe is, we have to look, and that means pushing the present frontiers of particle physics into uncharted territory. Right now, the community is debating between multiple approaches, with each one having its pros and cons. The nightmare scenario, however, isn’t that we’ll look and won’t find anything. It’s that infighting and a lack of unity will doom experimental physics forever, and that we won’t get a next-generation collider at all.

A hypothetical new accelerator, either a long linear one or one inhabiting a large tunnel beneath the Earth, could dwarf the sensitivity to new particles that prior and current colliders can achieve. Even at that, there’s no guarantee we’ll find anything new, but we’re certain to find nothing new if we fail to try. (ILC COLLABORATION)

When it comes to deciding what collider to build next, there are two generic approaches: a lepton collider (where electrons and positrons are accelerated and collided), and a proton collider (where protons are accelerated and collided). The lepton colliders have the advantages of:

the fact that leptons are point particles, rather than composite particles,
100% of the energy from electrons colliding with positrons can be converted into energy for new particles,
the signal is clean and much easier to extracts,
and the energy is controllable, meaning we can choose to tune the energy to a specific value and maximize the chance of creating a specific particle.

Lepton colliders, in general, are great for precision studies, and we haven’t had a cutting-edge one since LEP was operational nearly 20 years ago.

CERN LEP Collider

At various center-of-mass energies in electron/positron (lepton) colliders, various Higgs production mechanisms can be reached at explicit energies. While a circular collider can achieve much greater collision rates and production rates of W, Z, H, and t particles, a long-enough linear collider can conceivably reach higher energies, enabling us to probe Higgs production mechanisms that a circular collider cannot reach. This is the main advantage that linear lepton colliders possess; if they are low-energy only (like the proposed ILC), there is no reason not to go circular. (H. ABRAMOWICZ ET AL., EUR. PHYS. J. C 77, 475 (2017))

It’s very unlikely, unless nature is extremely kind, that a lepton collider will directly discover a new particle, but it may be the best bet for indirectly discovering evidence of particles beyond the Standard Model. We’ve already discovered particles like the W and Z bosons, the Higgs boson, and the top quark, but a lepton collider could both produce them in great abundances and through a variety of channels.

The more events of interest we create, the more deeply we can probe the Standard Model. The Large Hadron Collider, for example, will be able to tell whether the Higgs behaves consistently with the Standard Model down to about the 1% level. In a wide series of extensions to the Standard Model, ~0.1% deviations are expected, and the right future lepton collider will get you the best physics constraints possible.

The observed Higgs decay channels vs. the Standard Model agreement, with the latest data from ATLAS and CMS included. The agreement is astounding, and yet frustrating at the same time. By the 2030s, the LHC will have approximately 50 times as much data, but the precisions on many decay channels will still only be known to a few percent. A future collider could increase that precision by multiple orders of magnitude, revealing the existence of potential new particles.(ANDRÉ DAVID, VIA TWITTER)

These precision studies could be incredibly sensitive to the presence of particles or interactions we haven’t yet discovered. When we create a particle, it has a certain set of branching ratios, or probabilities that it will decay in a variety of ways. The Standard Model makes explicit predictions for those ratios, so if we create a million, or a billion, or a trillion such particles, we can probe those branching ratios to unprecedented precisions.

If you want better physics constraints, you need more data and better data. It isn’t just the technical considerations that should determine which collider comes next, but also where and how you can get the best personnel, the best infrastructure and support, and where you can build a (or take advantage of an already-existing) strong experimental and theoretical physics community.

The idea of a linear lepton collider has been bandied about in the particle physics community as the ideal machine to explore post-LHC physics for many decades, but that was under the assumption that the LHC would find a new particle other than the Higgs. If we want to do precision testing of Standard Model particles to indirectly search for new physics, a linear collider may be an inferior option to a circular lepton collider. (REY HORI/KEK)

There are two general classes proposals for a lepton collider: a circular collider and a linear collider. Linear colliders are simple: accelerate your particles in a straight line and collide them together in the center. With ideal accelerator technology, a linear collider 11 km long could reach energies of 380 GeV: enough to produce the W, Z, Higgs, or top in great abundance. With a 29 km linear collider, you could reach energies of 1.5 TeV, and with a 50 km collider, 3 TeV, although costs rise tremendously to accompany longer lengths.

Linear colliders are slightly less expensive than circular colliders for the same energy, because you can dig a smaller tunnel to reach the same energies, and they don’t suffer energy losses due to synchrotron radiation, enabling them to reach potentially higher energies. However, the circular colliders offer an enormous advantage: they can produce much greater numbers of particles and collisions.

Future Circular Collider (FCC)Larger LHC

The Future Circular Collider is a proposal to build, for the 2030s, a successor to the LHC with a circumference of up to 100 km: nearly four times the size of the present underground tunnels. This will enable, with current magnet technology, the creation of a lepton collider that can produce ~1⁰⁴ times the number of W, Z, H, and t particles that have been produced by prior and current colliders. (CERN / FCC STUDY)

While a linear collider might be able to produce 10 to 100 times as many collisions as a prior-generation lepton collider like LEP (dependent on energies), a circular version can surpass that easily: producing 10,000 times as many collisions at the energies required to create the Z boson.

Although circular colliders have substantially higher event rates than linear colliders at the relevant energies that produce Higgs particles as well, they begin to lose their advantage at energies required to produce top quarks, and cannot reach beyond that at all, where linear colliders become dominant.

Because all of the decay and production processes that occur in these heavy particles scales as either the number of collisions or the square root of the number of collisions, a circular collider has the potential to probe physics with many times the sensitivity of a linear collider.

A number of the various lepton colliders, with their luminosity (a measure of the collision rate and the number of detections one can make) as a function of center-of-mass collision energy. Note that the red line, which is a circular collider option, offers many more collisions than the linear version, but gets less superior as energy increases. Beyond about 380 GeV, circular colliders cannot reach, and a linear collider like CLIC is the far superior option. (GRANADA STRATEGY MEETING SUMMARY SLIDES / LUCIE LINSSEN (PRIVATE COMMUNICATION))

The proposed FCC-ee, or the lepton stage of the Future Circular Collider, would realistically discover indirect evidence for any new particles that coupled to the W, Z, Higgs, or top quark with masses up to 70 TeV: five times the maximum energy of the Large Hadron Collider.

The flipside to a lepton collider is a proton collider, which — at these high energies — is essentially a gluon-gluon collider. This cannot be linear; it must be circular.

The scale of the proposed Future Circular Collider (FCC), compared with the LHC presently at CERN and the Tevatron, formerly operational at Fermilab. The Future Circular Collider is perhaps the most ambitious proposal for a next-generation collider to date, including both lepton and proton options as various phases of its proposed scientific programme. (PCHARITO / WIKIMEDIA COMMONS)

There is really only one suitable site for this: CERN, since it not only needs a new, enormous tunnel, but all the infrastructure of the prior stages, which only exist at CERN. (They could be built elsewhere, but the cost would be more expensive than a site where the infrastructure like the LHC and earlier colliders like SPS already exist.)

The Super Proton Synchrotron (SPS), CERN’s second-largest accelerator.

Just as the LHC is presently occupying the tunnel previously occupied by LEP, a circular lepton collider could be superseded by a next-generation circular proton collider, such as the proposed FCC-pp. However, you cannot run both an exploratory proton collider and a precision lepton collider simultaneously; you must decommission one to finish the other.

The CMS detector at CERN, one of the two most powerful particle detectors ever assembled. Every 25 nanoseconds, on average, a new particle bunch collides at the center-point of this detector. A next-generation detector, whether for a lepton or proton collider, may be able to record even more data, faster, and with higher-precision than the CMS or ATLAS detectors can at present. (CERN)

It’s very important to make the right decision, as we do not know what secrets nature holds beyond the already-explored frontiers. Going to higher energies unlocks the potential for new direct discoveries, while going to higher precisions and greater statistics could provide even stronger indirect evidence for the existence of new physics.

The first-stage linear colliders are going to cost between 5 and 7 billion dollars, including the tunnel, while a proton collider of four times the LHC’s radius, with magnets twice as strong, 10 times the collision rate and next-generation computing and cryogenics might cost a total of up to $22 billion, offering as big a leap over the LHC as the LHC was over the Tevatron. Some money could be saved if we build the circular lepton and proton colliders one after the other in the same tunnel, which would essentially provide a future for experimental particle physics after the LHC is done running at the end of the 2030s.

The Standard Model particles and their supersymmetric counterparts. Slightly under 50% of these particles have been discovered, and just over 50% have never showed a trace that they exist. Supersymmetry is an idea that hopes to improve on the Standard Model, but it has yet to make successful predictions about the Universe in attempting to supplant the prevailing theory. However, new colliders are not being proposed to find supersymmetry or dark matter, but to perform generic searches. Regardless of what they’ll find, we’ll learn something new about the Universe itself. (CLAIRE DAVID / CERN)

The most important thing to remember in all of this is that we aren’t simply continuing to look for supersymmetry, dark matter, or any particular extension of the Standard Model. We have a slew of problems and puzzles that indicate that there must be new physics beyond what we currently understand, and our scientific curiosity compels us to look. In choosing what machine to build, it’s vital to choose the most performant machine: the ones with the highest numbers of collisions at the energies we’re interested in probing.

Regardless of which specific projects the community chooses, there will be trade-offs. A linear lepton collider can always reach higher energies than a circular one, while a circular one can always create more collisions and go to higher precisions. It can gather just as much data in a tenth the time, and probe for more subtle effects, at the cost of a lower energy reach.

Will it be successful? Regardless of what we find, that answer is unequivocally yes. In experimental physics, success does not equate to finding something, as some might erroneously believe. Instead, success means knowing something, post-experiment, that you did not know before you did the experiment. To push beyond the presently known frontiers, we’d ideally want both a lepton and a proton collider, at the highest energies and collision rates we can achieve.

There is no doubt that new technologies and spinoffs will come from whichever collider or colliders come next, but that’s not why we do it. We are after the deepest secrets of nature, the ones that will remain elusive even after the Large Hadron Collider finishes. We have the technical capabilities, the personnel, and the expertise to build it right at our fingertips. All we need is the political and financial will, as a civilization, to seek the ultimate truths about nature.

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“Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

From The New York Times: “It’s Intermission for the Large Hadron Collider”

From The New York Times

This is a special Augmented reality production of the NYT. Please view the original full article to take advantage of the 360 degree images inside the LHC.

DEC. 21, 2018
Dennis Overbye

The largest machine ever built is shutting down for two years of upgrades. Take an immersive tour of the collider and study the remnants of a Higgs particle in augmented reality.

CERN Control Center

MEYRIN, Switzerland — There is silence on the subatomic firing range.

A quarter-century ago, the physicists of CERN, the European Center for Nuclear Research, bet their careers and their political capital on the biggest and most expensive science experiment ever built, the Large Hadron Collider.

LHC

CERN map

CERN LHC Tunnel

CERN LHC particles

THE FOUR MAJOR PROJECT COLLABORATIONS

ATLAS

ALICE

CERN/ALICE Detector

CMS

LHCb

The collider is a kind of microscope that works by flinging subatomic particles around a 17-mile electromagnetic racetrack beneath the French-Swiss countryside, smashing them together 600 million times a second and sifting through the debris for new particles and forces of nature. The instrument is also a time machine, providing a glimpse of the physics that prevailed in the early moments of the universe and laid the foundation for the cosmos as we see it today.

The reward came in 2012 with the discovery of the Higgs boson, a long-sought particle that helps explain why there is mass, diversity and life in the cosmos.

CERN CMS Higgs Event

CERN ATLAS Higgs Event

The discovery was celebrated with champagne and a Nobel prize.

The collider will continue smashing particles and expectations for another 20 years. But first, an intermission. On December 3rd, the particle beams stopped humming. The giant magnets that guide the whizzing protons sighed and released their grip. The underground detectors that ring the tunnel stood down from their watch.

Over the next two years, during the first of what will be a series of shutdowns, engineers will upgrade the collider to make its beams more intense and its instruments more sensitive and discerning. And theoretical physicists will pause to make sense of the tantalizing, bewildering mysteries that the Large Hadron Collider has generated so far.

When protons collide

The collider gets its mojo from Einstein’s dictum that mass and energy are the same. The more energy that the collider can produce, the more massive are the particles created by the collisions. With every increase in the energy of their collider, CERN physicists are able to edge farther and farther back in time, closer to the physics of the Big Bang, when the universe was much hotter than today.

Inside CERN’s subterranean ring, some 10,000 superconducting electromagnets, powered by a small city’s worth of electricity, guide two beams of protons in opposite directions around the tunnel at 99.99999 percent of the speed of light, or an energy of 7 trillion electron volts. Those protons make the 17-mile circuit 11,000 times a second. (In physics, mass and energy are both expressed in terms of units called electron volts. A single proton, the building block of ordinary atoms, weighs about a billion electron volts.)

The protons enter the collider as atoms in a puff of hydrogen gas squirted from a bottle. As the atoms travel, electrical fields strip them of electrons, leaving bare, positively charged protons. These are sped up by a series of increasingly larger and more energetic electromagnets, until they are ready to enter the main ring of the collider.

When protons finally enter the main ring, they have been boosted into flying bombs of primordial energy, primed to smash apart — and recombine — when they strike their opposite numbers head-on, coming from the other direction.

The protons circulate inside vacuum pipes – one running clockwise, the other counterclockwise – and these are surrounded by superconducting electromagnets strung together around the tunnel like sausages. To generate enough force to bend the speeding protons, the magnets must be uncommonly strong: 8.3 Tesla, or more than a hundred thousand times stronger than Earth’s magnetic field — and more than strong enough to wreck a fancy Swiss watch.

Such a field in turn requires an electrical current of 12,000 amperes. That’s only feasible if the magnets are superconducting, meaning that electricity flows without expensive resistance. For that to happen, the magnets must be supercold; they are bathed in 150 tons of superfluid helium at a temperature of 1.9 Kelvin, making the Large Hadron Collider literally one of the coldest places in the universe.

If things go wrong down here, they can go very wrong. In 2008, as the collider was still being tuned up, the link between a pair of magnets exploded, delaying operations for almost two years.

The energy stored in the magnetic fields is equivalent to a fully loaded jumbo jet going 500 miles per hour; if a magnet loses its cool and heats up, all that energy must go someplace. And the proton beam itself can cut through many feet of steel.

A tale of four detectors

The beams cross at four points around the racetrack.

At each juncture, gigantic detectors — underground mountains of electronics, cables, computers, pipes, magnets and even more magnets — have been erected. The two biggest and most expensive experiments, CMS (the Compact Muon Solenoid) and Atlas (A Toroidal L.H.C. Apparatus) sit, respectively, at the noon and 6 o’clock positions of the circular track.

Wrapped around them, like the layers of an onion, are instruments designed to measure every last spark of energy or matter that might spew from the collision. Silicon detectors track the paths of lightweight, charged particles such as electrons. Scintillation crystals capture the energies of gamma rays. Chambers of electrified gas track more far-flung particles. And powerful magnets bend the paths of these particles so that their charges and masses can be determined.

The proton beams cross 40 million times per second in each of the four detectors, resulting in about a billion actual collisions every second.

What’s the antimatter?

Why is there something instead of nothing in the universe?

Answering that question is the mission of the detector known as LHCb, which sits at about 4 o’clock on the collider dial. The “b” stands for beauty — and for the B meson, a subatomic particle that is crucial to the experiment.

When matter is created — in a collider, in the Big Bang — equal amounts of matter and its opposite, antimatter, should be formed, according to the laws of physics As We Know Them. When matter and antimatter meet, they annihilate each other, producing energy.

By that logic, when matter and antimatter formed in the Big Bang, they should have cancelled out each other, leaving behind an empty universe. But it’s not empty: We are here, and our antimatter is not.

Why not? Physicists suspect that some subtle imbalance between matter and antimatter is responsible. The LHCb experiment looks for that imbalance in the behavior of B mesons, which are often sprayed from the proton collisions.

B mesons have an exotic property: They flicker back and forth between being matter and antimatter. Sensors record their passage through the LHCb room, seeking differences between the particles and their antimatter twins. Any discrepancy between the two could be a clue to why matter flourished billions of years ago and antimatter perished.

Turning back the cosmic clock

At about 8 o’clock on the collider dial is Alice, another detector with a special purpose. It, too, is fixed on the distant past: the brief moment a couple of microseconds after the Big Bang, before the first protons and neutrons congealed out of a “primordial soup” of quarks and gluons.

Alice’s job is to study tiny droplets of that distant past that are created when the collider bangs together lead ions instead of protons. Researchers expected this material, known in the lingo as a quark-gluon plasma, to behave like a gas, but it turns out to behave more like a liquid.

Sifting the data

The collider’s enormous detectors are like 100 megapixel cameras that take 40 million pictures a second. Most of the data from that deluge is immediately thrown away. Triggers, programmed to pick out events that physicists thought might be interesting, save only about a thousand collision events per second. Even still, an enormous pool of data winds up in the CERN computer banks.

CERN DATA Center

According to the casino rules of modern quantum physics, anything that can happen will happen eventually. Before a single proton is fired through the collider, computers have calculated all the possible outcomes of a collision according to known physics. Any unexpected bump in the real data at some energy could be a signal of unknown physics, a new particle.

That was how the Higgs was discovered, emerging from the statistical noise in the autumn of 2011. Only one of every 10 billion collisions creates a Higgs boson. The Higgs vanishes instantly and can’t be observed directly, but it decays into fragments that can be measured and identified.

What eventually stood out from the data was evidence for a particle that weighs all by itself as much as an iodine atom: a flake of an invisible force field that permeates space like molasses, impeding motion and assigning mass to objects that pass through it.

And so in 2012, after half a century and billions of dollars, thousands of physicists toasted over champagne. Peter Higgs, for whom the elusive boson was named, shared the Nobel prize with François Englert, who had independently predicted the particle’s existence.

Peter Higgs

François Englert

An intermission underground

The current shutdown is the first of a pair of billion-dollar upgrades intended to boost the productivity of the Large Hadron Collider tenfold by the end of the decade.

The first shutdown will last for two years, until 2021; during that time, engineers will improve the series of smaller racetracks that speed up protons and inject them into the main collider. The collider then will run for two years and shut down again, in 2024, for two more years, so that engineers can install new magnets to intensify the proton beams and collisions.

Reincarnated in 2026 as the High Luminosity L.H.C., the collider is scheduled to run for another decade, until 2035 or so, which means its career probing the edge of human knowledge is still beginning.

Judging by the collider’s productivity, measured in terms of trillions of subatomic smashups, more than 95 percent of its scientific potential lies ahead.

Both the Atlas and CMS experiments will receive major upgrades during the next two shutdowns, including new silicon trackers, to replace the olds ones burned out by radiation.

To keep up with the increased collision rate, both Atlas and CMS have had to upgrade the finicky trigger systems that decide which collision events to keep and study. Currently, of a billion events per second, they can keep 1,500; the upgrade will raise that figure to 10,000.

And what a flow of collisions it will be. Physicists measure the productivity, or luminosity, of their colliders in terms of collisions. It took about 3,000 trillion collisions to confirm the Higgs boson. As of the December shutdown the collider had logged about 20,000 trillion collisions. But those were, and are, early days.

By 2037, the Large Hadron Collider should have produced roughly 4 million trillion primordial fireballs, bristling with who knows what. The whole universe is still up for grabs.

After the Higgs

Discovering the Higgs was an auspicious start. But the champagne came with a mystery.

Over the last century, physicists have learned to explain some of the grandest and subtlest phenomena in nature — the arc of a rainbow, the scent of a gardenia, the twitch of a cat’s whiskers — as a handful of elementary particles interacting through four basic forces, playing a game of catch with force-carrying particles called bosons according to a set of equations called the Standard Model.

The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

But why these particles and these forces? Why is the universe made of matter but not antimatter? What happens at the center of a black hole, or happened at the first instant of the Big Bang? If the Higgs boson determines the masses of particles, what determines the mass of the Higgs?

Who, in other words, watches the watchman?

The Standard Model, for all its brilliance and elegance, does not say. Particles that might answer these questions have not shown up yet in the collider. Fabiola Gianotti, the director-general of CERN, expressed surprise. “I would have expected new physics to manifest itself at the energy scale of the Large Hadron Collider,” she said.

Some physicists have responded by speculating about multiple universes and other exotic phenomena. Some clues, Dr. Gianotti said, might come from studying the new particle on the block, the Higgs.

“We physicists are happy when we understand things, but we are even happier when we don’t understand,” she said. “And today we know that we don’t understand everything. We know that we are missing something important and fundamental. And this is very exciting.”

Colliders of tomorrow

Humans soon must decide which machines, if any, will be built to augment or replace the Large Hadron Collider. That collider had a “killer app” of sorts: it was designed to achieve an energy at which, according to the prediction of the Standard Model, the Higgs or something like it would become evident and provide an explanation for particle masses.

But the Standard Model doesn’t predict a new keystone particle in the next higher energy range. Luckily, nobody believes the Standard Model is the last word about the universe, but as the machines increase in energy, particle physicists will be shooting in the dark.

For a long time, the leading candidate for Next Big Physics Machine has been the International Linear Collider, which would fire electrons and their antimatter opposites, positrons, at each other.

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

The collisions would produce showers of Higgs bosons. The experiment would be built in Japan, if it is built at all, but Japan has yet to commit to hosting the project, which would require them to pay for about half of the $5.5 billion cost- see https://sciencesprings.wordpress.com/2018/12/21/from-nature-via-ilc-plans-for-worlds-next-major-particle-collider-dealt-big-blow.

In the meantime, Europe has convened meetings and workshops to decide on a plan for the future of particle physics there. “If there is no word from Japan by the end of the year, then the I.L.C. will not figure in the next five-year plan for Europe,” Lyn Evans, a CERN physicist who was in charge of building the Large Hadron Collider, said in an email.

CERN has proposed its own version of a linear collider, the Compact Linear Collider, that could be scaled up gradually from Higgs bosons to higher energies. Also being considered is a humongous collider, 100 kilometers around, that would lie under Lake Geneva and would reach energies of 100 trillion electron volts — seven times the power of the Large Hadron Collider.

Cern Compact Linear Collider

CLC map

CLC TWO-BEAM ACCELERATION TEST STAND

And in November the Chinese Academy of Sciences released the design for a next-generation collider of similar size, called the Circular Electron Positron Collider.

China Circular Electron Positron Collider (CEPC) map

China Circular Electron-Positron collider depiction

The machine could be the precursor for a still more powerful machine that has been dubbed the Great Collider. Politics and economics, as well as physics, will decide which, if any, of these machines will see a shovel.

“If we want a new machine, nothing is possible before 2035,” Frederick Bordry, CERN’s director of accelerators, said of European plans. Building such a machine is a true human adventure, he said: “Twenty-five years to build and another 25 to operate.”

Noting that he himself is 64, he added, “I’m working for the young people.”

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From Nature via ILC: “Plans for world’s next major particle collider dealt big blow”

From ILC.

19 December 2018
Elizabeth Gibney

Nature

Plans to build a particle smasher in Japan to succeed the Large Hadron Collider have suffered a significant setback. An influential report by Japanese scientists concluded that they could not support plans to build the International Linear Collider (ILC) in the country.

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

The facility has been decades in design and would study the Higgs boson, which was discovered in 2012 and is the last puzzle piece in particle physicists’ ‘standard model’.

The discoveries predicted to come out of the ILC would not fully warrant its nearly US$7-billion cost, said a committee of the Science Council of Japan in a report released on 19 December, according to press reports. As host, Japan might be expected to pay as much as half of the total. The committee, which advises the government, added that uncertainty about whether international partners would share the project’s costs increased its concerns.

The proposed accelerator — which would be more than 20 kilometres long — would enable physicists to detect the products of precise collisions between electrons and their antimatter counterparts, positrons.

Government advice

The government will now use the report, which reflects the views of the academic community in Japan and not just those of high-energy physicists, to guide its decision on whether to host the facility. A decision is expected by 7 March, when the international group overseeing the ILC’s development, the Linear Collider Board, meets in Tokyo.

Physicists expressed concern at the committee’s conclusions. “This is very bad news, as this makes it very unlikely that the #ILC will be build in Japan — and probably at all,” tweeted Axel Maas, a theoretical physicist at the University of Graz in Austria.

However, the committee did state that the scientific case for building the ILC was sound, says Hitoshi Yamamoto, a physicist at Tohoku University in Sendai and a member of the ILC collaboration. It also acknowledged that the collider is seen in the particle-physics community as the top priority among possible future projects, he adds.

The project now needs some good news, says Yamamoto. With funding tight around the world, “the situation for the ILC is getting worse rapidly”, he says. “A positive announcement by the Japanese government will reverse the trend and suddenly bring the ILC as the top item on the table,” says Yamamoto.

Any concern that other areas of science in Japan could suffer if the costly project goes ahead is understandable, says Brian Foster, a physicist at the University of Oxford, UK, and part of the team designing the facility. But he says the council’s pessimistic take does not necessarily mean the government will not support the project. “If the government wants to do it, it will,” he says.

Sole nation

Japan is the only nation so far to show interest in the collider, and a decision on whether it will host the facility is long overdue. Japanese physicists pitched to the international community to build the facility in Japan in 2012, after scientists at the LHC — based at CERN, Europe’s particle-physics lab near Geneva — discovered the Higgs boson, a particle involved in the mechanism by which all others get mass.

Physicists wanted to use the new facility to study any phenomena that the LHC might discover. They know that the standard model is incomplete and hope that unknown higher-energy particles could help explain long-standing mysteries such as the nature of dark matter.

But plans for the collider have stagnated because no nations have offered funding, and because of the LHC’s failure to find any new phenomena beyond the Higgs. In 2017 physicists scaled back their ambitions for the ILC, proposing a shorter, lower-energy design that would focus on the Higgs alone.

To physicists, a ‘Higgs factory’ would still be hugely valuable. As electron and positrons are fundamental particles, their collisions would be cleaner than the proton–proton collisions at the LHC. By targeting collisions at the right energy, the planned collider would produce millions of Higgs bosons for studies that could reveal new physics indirectly, by exploring how the Higgs boson interacts with other known particles.

Researchers in China, who recently proposed to build a 100-kilometre ring-shaped Higgs factory, will also examine the report carefully. They need funding from both Chinese and foreign governments to build the facility. Although particle physicists would like to see both experiments built, international partners are likely to fund only one Higgs factory. If the ILC receives the backing of the high energy physics community, that may shorten the odds on the Chinese collider being built, although the country could also go it alone.

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The International Linear Collider (ILC) is a proposed linear particle accelerator.It is planned to have a collision energy of 500 GeV initially, with the possibility for a later upgrade to 1000 GeV (1 TeV). The host country for the accelerator has not yet been chosen and proposed locations are Japan, Europe (CERN) and the USA (Fermilab). Japan is considered the most likely candidate, as the Japanese government is willing to contribute half of the costs, according to a representative for the European Commission on Future Accelerators.Construction could begin in 2015 or 2016 and will not be completed before 2026.

From Interactions.org: ““Unshakable conviction” of scientific case of the International Linear Collider”

From Interactions.org

ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan

Scientists gathering in Arlington, Texas, U.S.A., for the International Workshop on Future Linear Colliders (LCWS2018), a scientific conference about future international particle physics projects, issued a statement (the ‘Texas statement’) expressing their strong commitment to do whatever necessary for the realisation of the International Linear Collider (ILC) in Japan. Having stressed the scientific case and the technological merits of the ILC through the statements issued during a scientific workshop in Tokyo in 2015, and in Fukuoka in May 2018, participants of LCWS2018 on behalf of the global Linear Collider Collaboration (LCC) express their unshakable conviction about the ILC and their determination to bring it to its fruition.

“The Texas Statement” – Statement on the ILC Higgs Factory
Scientists from all over the world are now gathering together at the International Workshop on Future Linear Colliders (LCWS2018) held in Arlington, Texas, with a firm determination to make the ILC a reality. Together with colleagues around the world, we hereby issue this ‘Texas Statement’ with unshakable conviction on its scientific case and to express our strong commitment to do whatever necessary for its success.

The ILC is the right new experimental facility to advance our understanding of the Universe. The ILC project has been developed by an international collaboration over three decades. We conceived it as the machine to lead the era of particle physics at the Terascale with the Higgs particle as the centerpiece. The discovery of the Higgs particle by the LHC fixed the needed energy, and we now have a concrete plan for the ILC Higgs factory. Subsequent measurements at the LHC further reinforced the importance of the precision Higgs studies. If scientifically justified by the findings of the precision Higgs study, the collision energy of the ILC can be easily upgraded. Throughout the period of ILC development, our original motivation has become increasingly clearer and stronger.

The ILC is a source of new innovative technologies. We also pride ourselves in the technology for the ILC. Global collaboration has made enormous progress in the development of the superconducting acceleration technology, improving its performance by quantum leaps. This technology, developed for the ILC, is now essential, for example, for the current state-of-the-art X-ray and neutron facilities. More innovations broadly benefitting science and society are in store as we proceed along our path.
Now is the time to move forward. The international community represented by the participants of LCWS2018 is committed to bring the ILC to its fruition. Once the expression of intention to host the ILC is issued by the Japanese government, we will greatly expand our own efforts and work with our respective governments ever more intensively to help achieve the necessary international agreements. We eagerly await the signal to proceed and, when the ILC starts in earnest, we will be ready to carry through on its promise.

Scientists attending LCWS2018
on behalf of the global Linear Collider Collaboration
Background information:
The International Linear Collider is a proposed particle accelerator whose mission is to carry out research about the fundamental particles and forces that govern the Universe. It would complement the Large Hadron Collider at CERN, where the Higgs boson was discovered in 2012, and shed more light on the discoveries scientists have made and are likely to make there in the coming years. The ILC will be one of the world’s largest and most sophisticated scientific endeavours. The realisation of the ILC will require truly global participation.
The Linear Collider Collaboration consists of scientists and engineers working on the Compact Linear Collider Study (CLIC) and the International Linear Collider (ILC). It is headed by former LHC Project Director Lyn Evans and coordinates the world-wide research and development for accelerators and detectors.

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