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  • richardmitnick 3:42 pm on February 12, 2018 Permalink | Reply
    Tags: , Aleksandra Dimitrievska, , , CERN LHC, , , , ,   

    From LBNL- “From Belgrade to Berkeley: A Postdoctoral Researcher’s Path in Particle Physics” 

    Berkeley Logo

    Berkeley Lab

    February 12, 2018

    Berkeley Lab’s Aleksandra Dimitrievska is working on a next-gen particle detector for CERN’s Large Hadron Collider

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    Aleksandra Dimitrievska works on prototype chips for a planned upgrade at CERN’s Large Hadron Collider. (Credit: Marilyn Chung/Berkeley Lab)

    After completing her Ph.D. thesis in calculating the mass of the W boson – an elementary particle that mediates one of the universe’s fundamental forces – physics researcher Aleksandra Dimitrievska is now testing out components for a scheduled upgrade of the world’s largest particle detectors.

    Dimitrievska left the University of Belgrade in Serbia late last year to join the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) as the recipient of an Owen Chamberlain Postdoctoral Fellowship in Experimental Particle Physics & Cosmology in the Lab’s Physics Division. The fellowship will extend up to five years.

    “Before, I was working behind a computer on coding. Now, I am in a clean room making wire bonds on computer chips, so it’s a much different experience,” Dimitrievska said. “I completely feel like a physicist now.”

    The Chamberlain Fellowship was created in 2002 to honor the late Owen Chamberlain, a Berkeley Lab physicist and UC Berkeley professor who received the Nobel Prize in Physics in 1959 for his work on the team that discovered the anti-proton using the Lab’s Bevatron accelerator. He also worked on the development of the time projection chamber, a type of detector that has been widely used in particle physics experiments.

    Dimitrievska’s path toward a career in particle physics led her to CERN’s Large Hadron Collider (LHC), a particle collider with an underground tunnel measuring 17 miles in circumference that is used to accelerate protons up to nearly the speed of light and collide them in detectors to measure the ensuing subatomic fireworks.

    “I started as a summer student at CERN in 2012. After that I went back to Belgrade – my Ph.D. advisor was involved in work on the W boson mass measurement,” she said. He connected her with a CERN team led by French physicist Maarten Boonekamp.

    The W boson and Z boson, which were both discovered in CERN experiments in 1983, are carriers of the “weak force” that is responsible for the particle process triggering fusion in the sun and other stars, the presence of radiation across the universe, and the breakdown of radioactive elements via a process known as beta decay. The W boson can have a positive or negative charge while the Z boson has a neutral charge, and each of these particles has a mass that is heavier than an iron atom.

    But despite such large masses, it has been difficult to pinpoint the W boson’s mass because of the typical noisy mess of other particle processes associated with its creation in collider experiments.

    “This is a really difficult measurement,” Dimitrievska said. The W boson’s mass must be calculated based on indirect measurements – a careful dissection of the data from related particle processes including recoil, in which particles are ejected from other particles in high-energy collisions at the LHC.

    “We started from scratch, one step at a time,” she said, to find the best way to calibrate the W boson measurements. “We tried different approaches and different ideas. The most important things are the uncertainties,” she said, and in finding ways to reduce the uncertainties in the analyses of data from experiments. “It takes a lot of time to really calibrate each source.”

    The team conducting the analysis found that a useful way to measure the W boson is to use measurements of the Z boson for calibration. “You are calibrating the recoil on the Z boson events, and then you extrapolate (measurements) for the W boson,” she said, based in part on the uncertainties in the Z boson measurements.

    The team worked with data from millions of particle collisions that produced candidate W bosons in the 2011 run of the LHC. Ongoing studies will apply the same techniques developed for the 2011 analysis for larger sets of data accumulated at the LHC in 2012, 2015, and 2016. The latest sets of LHC data, because they can involve larger numbers of colliding protons, are even more challenging to pick through in isolating individual particle properties.

    Such painstaking analyses can ultimately test whether the standard model of particle physics, developed through decades of experiments and theories, holds up to increasingly precise measurements.

    In this case, Dimitrievska’s team found good agreement in their measurements with the standard model. “There is no hint of physics beyond the standard model, but this result is important because we have something new to put in front of the theoretical ideas and see where there is place for improvement in the measurements,” she said.

    She added, “The calibration and methods we used will also be used for other measurements at higher energies.”

    The latest measurement, published Feb. 6 in the European Physical Journal C, determined the mass of the W boson to be about 80,370 mega (million) electronvolts, or MeV, with a statistical uncertainty of plus or minus 7 MeV, which is consistent with an average from previous measurements of about 80,385 MeV, with uncertainty at plus or minus 15 MeV. An electronvolt is a unit of energy that is a common measure of mass for subatomic particles.

    Dimitrievska successfully defended her Ph.D. thesis on the W boson mass measurement at the University of Belgrade in December.

    Her current work at Berkeley Lab is focused on testing 2-centimeter-by-1-centimeter prototype computer chips for the planned High-Luminosity LHC at CERN that will produce a higher volume of particle collisions and data.

    “Because we will have more data, the readout system has to be faster,” she said. “Basically, we have to improve everything.”

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    Aleksandra Dimitrievska holds a prototype chip for planned detector upgrades at CERN. (Credit: Marilyn Chung/Berkeley Lab)

    The final version of the chips that she is testing will be installed in the inner part of the ATLAS and CMS detectors at CERN and must be radiation-hardened to withstand the constant drumming of high-energy particles. She has used 3-D printers at UC Berkeley to fabricate prototype components related to the chip assemblies she works with.

    “For now, I am just testing if the chips work – how they are collecting data,” she said. A next step for her research group is to set up a particle beam to monitor how the chips perform under simulated experimental conditions.

    As an active member of Berkeley Lab’s ATLAS collaboration team, Dimitrievska also participates remotely in several meetings per week hosted at CERN, and she said she looks forward to the opportunity to work on the LHC upgrade project as it moves forward from its R&D stages to actual fabrication, assembly, and installation.

    “I think this is the really nice part about this work,” she said. “You can see the development of something that you can actually use later. You can participate first in the development of the detector, and then do the analysis and see how it really works.”

    See the full article here .

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  • richardmitnick 12:54 pm on January 30, 2018 Permalink | Reply
    Tags: , , CERN LHC, , , , , , ,   

    From LBNL: “Applying Machine Learning to the Universe’s Mysteries” 

    Berkeley Logo

    Berkeley Lab

    Glenn Roberts Jr.
    geroberts@lbl.gov
    (510) 486-5582

    1
    The colored lines represent calculated particle tracks from particle collisions occurring within Brookhaven National Laboratory’s STAR detector at the Relativistic Heavy Ion Collider, and an illustration of a digital brain. The yellow-red glow at center shows a hydrodynamic simulation of quark-gluon plasma created in particle collisions. (Credit: Berkeley Lab)

    BNL/RHIC Star Detector

    Computers can beat chess champions, simulate star explosions, and forecast global climate. We are even teaching them to be infallible problem-solvers and fast learners.

    And now, physicists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and their collaborators have demonstrated that computers are ready to tackle the universe’s greatest mysteries. The team fed thousands of images from simulated high-energy particle collisions to train computer networks to identify important features.

    The researchers programmed powerful arrays known as neural networks to serve as a sort of hivelike digital brain in analyzing and interpreting the images of the simulated particle debris left over from the collisions. During this test run the researchers found that the neural networks had up to a 95 percent success rate in recognizing important features in a sampling of about 18,000 images.

    The study was published Jan. 15 in the journal Nature Communications.

    The researchers programmed powerful arrays known as neural networks to serve as a sort of hivelike digital brain in analyzing and interpreting the images of the simulated particle debris left over from the collisions. During this test run the researchers found that the neural networks had up to a 95 percent success rate in recognizing important features in a sampling of about 18,000 images.

    The next step will be to apply the same machine learning process to actual experimental data.

    Powerful machine learning algorithms allow these networks to improve in their analysis as they process more images. The underlying technology is used in facial recognition and other types of image-based object recognition applications.

    The images used in this study – relevant to particle-collider nuclear physics experiments at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider and CERN’s Large Hadron Collider – recreate the conditions of a subatomic particle “soup,” which is a superhot fluid state known as the quark-gluon plasma believed to exist just millionths of a second after the birth of the universe. Berkeley Lab physicists participate in experiments at both of these sites.

    BNL RHIC Campus

    BNL/RHIC

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    “We are trying to learn about the most important properties of the quark-gluon plasma,” said Xin-Nian Wang, a nuclear physicist in the Nuclear Science Division at Berkeley Lab who is a member of the team. Some of these properties are so short-lived and occur at such tiny scales that they remain shrouded in mystery.

    In experiments, nuclear physicists use particle colliders to smash together heavy nuclei, like gold or lead atoms that are stripped of electrons. These collisions are believed to liberate particles inside the atoms’ nuclei, forming a fleeting, subatomic-scale fireball that breaks down even protons and neutrons into a free-floating form of their typically bound-up building blocks: quarks and gluons.

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    The diagram at left, which maps out particle distribution in a simulated high-energy heavy-ion collision, includes details on particle momentum and angles. Thousands of these images were used to train and test a neural network to identify important features in the images. At right, a neural network used the collection of images to created this “importance map” – the lighter colors represent areas that are considered more relevant to identify equation of state for the quark-gluon matter created in particle collisions. (Credit: Berkeley Lab)

    Researchers hope that by learning the precise conditions under which this quark-gluon plasma forms, such as how much energy is packed in, and its temperature and pressure as it transitions into a fluid state, they will gain new insights about its component particles of matter and their properties, and about the universe’s formative stages.

    But exacting measurements of these properties – the so-called “equation of state” involved as matter changes from one phase to another in these collisions – have proven challenging. The initial conditions in the experiments can influence the outcome, so it’s challenging to extract equation-of-state measurements that are independent of these conditions.

    “In the nuclear physics community, the holy grail is to see phase transitions in these high-energy interactions, and then determine the equation of state from the experimental data,” Wang said. “This is the most important property of the quark-gluon plasma we have yet to learn from experiments.”

    Researchers also seek insight about the fundamental forces that govern the interactions between quarks and gluons, what physicists refer to as quantum chromodynamics.

    Long-Gang Pang, the lead author of the latest study and a Berkeley Lab-affiliated postdoctoral researcher at UC Berkeley, said that in 2016, while he was a postdoctoral fellow at the Frankfurt Institute for Advanced Studies, he became interested in the potential for artificial intelligence (AI) to help solve challenging science problems.

    He saw that one form of AI, known as a deep convolutional neural network – with architecture inspired by the image-handling processes in animal brains – appeared to be a good fit for analyzing science-related images.

    “These networks can recognize patterns and evaluate board positions and selected movements in the game of Go,” Pang said. “We thought, ‘If we have some visual scientific data, maybe we can get an abstract concept or valuable physical information from this.’”

    Wang added, “With this type of machine learning, we are trying to identify a certain pattern or correlation of patterns that is a unique signature of the equation of state.” So after training, the network can pinpoint on its own the portions of and correlations in an image, if any exist, that are most relevant to the problem scientists are trying to solve.

    Accumulation of data needed for the analysis can be very computationally intensive, Pang said, and in some cases it took about a full day of computing time to create just one image. When researchers employed an array of GPUs that work in parallel – GPUs are graphics processing units that were first created to enhance video game effects and have since exploded into a variety of uses – they cut that time down to about 20 minutes per image.

    They used computing resources at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC) in their study, with most of the computing work focused at GPU clusters at GSI in Germany and Central China Normal University in China.

    NERSC Cray XC40 Cori II supercomputer

    LBL NERSC Cray XC30 Edison supercomputer


    The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

    NERSC PDSF


    PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

    A benefit of using sophisticated neural networks, the researchers noted, is that they can identify features that weren’t even sought in the initial experiment, like finding a needle in a haystack when you weren’t even looking for it. And they can extract useful details even from fuzzy images.

    “Even if you have low resolution, you can still get some important information,” Pang said.

    Discussions are already underway to apply the machine learning tools to data from actual heavy-ion collision experiments, and the simulated results should be helpful in training neural networks to interpret the real data.

    “There will be many applications for this in high-energy particle physics,” Wang said, beyond particle-collider experiments.

    Also participating in the study were Kai Zhou, Nan Su, Hannah Petersen, and Horst Stocker from the following institutions: Frankfurt Institute for Advanced Studies, Goethe University, GSI Helmholtzzentrum für Schwerionenforschung (GSI), and Central China Normal University. The work was supported by the U.S Department of Energy’s Office of Science, the National Science Foundation, the Helmholtz Association, GSI, SAMSON AG, Goethe University, the National Natural Science Foundation of China, the Major State Basic Research Development Program in China, and the Helmholtz International Center for the Facility for Antiproton and Ion Research.

    NERSC is DOE Office of Science user facility.

    See the full article here .

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  • richardmitnick 12:47 pm on January 18, 2018 Permalink | Reply
    Tags: , CERN LHC, , Long-lived physics, MATHUSLA- Massive Timing Hodoscope for Ultra Stable Neutral Particles, ,   

    From CERN: “Long-lived physics” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    18 Jan 2018
    Iva Raynova

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    The CMS experiment is looking for exotic long-lived particles that could get trapped in its detector layers (Image: Michael Hoch, Maximilien Brice/CERN)

    New particles produced in the LHC’s high-energy proton-proton collisions don’t hang around for long. A Higgs boson exists for less than a thousandth of a billionth of a billionth of a second before decaying into lighter particles, which can then be tracked or stopped in our detectors. Nothing rules out the existence of much longer-lived particles though, and certain theoretical scenarios predict that such extraordinary objects could get trapped in the LHC detectors, sitting there quietly for days.

    The CMS collaboration has reported new results [JHEP] in its search for heavy long-lived particles (LLPs), which could lose their kinetic energy and come to a standstill in the LHC detectors. Provided that the particles live for longer than a few tens of nanoseconds, their decay would be visible during periods when no LHC collisions are taking place, producing a stream of ordinary matter seemingly out of nowhere.

    The CMS team looked for these types of non-collision events in the densest detector materials of the experiment, where the long-lived particles are most likely to be stopped, based on LHC collisions in 2015 and 2016. Despite scouring data from a period of more than 700 hours, nothing strange was spotted. The results set the tightest cross-section and mass limits for hadronically-decaying long-lived particles that stop in the detector to date, and the first limits on stopped long-lived particles produced in proton-proton collisions at an energy of 13 TeV.

    The Standard Model, the theoretical framework that describes all the elementary particles, was vindicated in 2012 with the discovery of the Higgs boson.

    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.


    Standard Model of Particle Physics from Symmetry Magazine

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    But some of the universe’s biggest mysteries remain unexplained, such as why matter prevailed over antimatter in the early universe or what exactly dark matter is. Long-lived particles are among numerous exotic species that would help address these mysteries and their discovery would constitute a clear sign of physics beyond the Standard Model. In particular, the decays searched for in CMS concerned long-lived gluinos arising in a model called “split” supersymmetry (SUSY) and exotic particles called “MCHAMPs”.

    While the search for long-lived particles at the LHC is making rapid progress at both CMS and ATLAS, the construction of a dedicated LLP detector has been proposed for the high-luminosity era of the LHC. MATHUSLA (Massive Timing Hodoscope for Ultra Stable Neutral Particles) is planned to be a surface detector placed 100 metres above either ATLAS or CMS.

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    It would be an enormous (200 × 200 × 20 m) box, mostly empty except for the very sensitive equipment used to detect LLPs produced in LHC collisions.

    Since LLPs interact weakly with ordinary matter, they will experience no trouble travelling through the rocks between the underground experiment and MATHUSLA. This process is similar to how weakly interacting cosmic rays travel through the atmosphere and pass through the Earth to reach our underground detectors, only in reverse. If constructed, the experiment will explore many more scenarios and bring us closer to discovering new physics.

    See the full article here.

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    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

    Quantum Diaries

     
  • richardmitnick 2:52 pm on January 16, 2018 Permalink | Reply
    Tags: , CERN LHC, , , , , , , The Dark Sector   

    From Symmetry: “Voyage into the dark sector” 

    Symmetry Mag

    Symmetry

    01/16/18
    Sarah Charley

    1
    Artwork by Sandbox Studio, Chicago with Ana Kova

    A hidden world of particles awaits. [We hope!]

    We don’t need extra dimensions or parallel universes to have an alternate reality superimposed right on top of our own. Invisible matter is everywhere.

    For example, take neutrinos generated by the sun, says Jessie Shelton, a theorist at the University of Illinois at Urbana-Champaign who works on dark sector physics. “We are constantly bombarded with neutrinos, but they pass right through us. They share the same space as our atoms but almost never interact.”

    As far as scientists can tell, neutrinos are solitary particles. But what if there is a whole world of particles that interact with one another but not with ordinary atoms? This is the idea behind the dark sector: a theoretical world of matter existing alongside our own but invisible to the detectors we use to study the particles we know.

    “Dark sectors are, by their very definition, built out of particles that don’t interact strongly with the Standard Model,” Shelton says.

    The Standard Model is a physicist’s field guide to the 17 particles and forces that make up all visible matter.

    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.

    Standard Model of Particle Physics from Symmetry Magazine

    It explains how atoms can form and why the sun shines. But it cannot explain gravity, the cosmic imbalance of matter and antimatter, or the disparate strengths of nature’s four forces.

    CERN ALPHA Antimatter Factory

    On its own, an invisible world of dark sector particles cannot solve all these problems. But it certainly helps.

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    Artwork by Sandbox Studio, Chicago with Ana Kova

    The main selling point for the dark sector is that the theories comprehensively confront the problem of dark matter. Dark matter is a term physicists coined to explain bizarre gravitational effects they observe in the cosmos. Distant starlight appears to bend around invisible objects as it traverses the cosmos, and galaxies spin as if they had five times more mass than their visible matter can explain. Even the ancient light preserved in cosmic microwave background seems to suggest that there is an invisible scaffolding on which galaxies are formed.

    Some theories suggest that dark matter is simple cosmic debris that adds mass—but little else—to the complexity of our cosmos. But after decades of searching, physicists have yet to find dark matter in a laboratory experiment. Maybe the reason scientists haven’t been able to detect it is that they’ve been underestimating it.

    “There is no particular reason to expect that whatever is going on in the dark sector has to be as simple as our most minimal models,” Shelton says. “After all, we know that our visible world has a lot of rich physics: Photons, electrons, protons, nuclei and neutrinos are all critically important for understanding the cosmology of how we got here. The dark sector could be a busy place as well.”

    According to Shelton, dark matter could be the only surviving particle out of a similarly complicated set of dark particles.

    “It could even be something like the proton, a bound state of particles interacting via a very strong dark force. Or it could even be something like a hydrogen atom, a bound state of particles interacting via a weaker dark force,” she says.

    Even if terrestrial experiments cannot see these stable dark matter particles directly, they might be sensitive to other kinds of dark particles, such as dark photons or short-lived dark particles that interact strongly with the Higgs boson.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    “The Higgs is one of the easiest ways for the Standard Model particles to talk to the dark sector,” Shelton says.

    As far as scientists know, the Higgs boson is not picky. It may very well interact will all sorts of massive particles, including those invisible to ordinary atoms. If the Higgs boson interacts with massive dark sector particles, scientists should find that its properties deviate slightly from the Standard Model’s predictions. Scientists at the Large Hadron Collider are precisely measuring the properties of the Higgs boson to search for unexpected quirks that could open a gateway to new physics.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    At the same time, scientists are also using the LHC to search for dark sector particles directly. One theory is that at extremely high temperatures, dark matter and ordinary matter are not so different and can transform into one another through a dark force. In the hot and dense early universe, this would have been quite common.

    “But as the universe expanded and cooled, this interaction froze out, leaving some relic dark matter behind,” Shelton says.

    The energetic particle collisions generated by the LHC imitate the conditions that existed in the early universe and could unlock dark sector particles. If scientists are lucky, they might even catch dark sector particles metamorphosing into ordinary matter, an event that could materialize in the experimental data as particle tracks that suddenly appear from no apparent source.

    But there are also several feasible scenarios in which any interactions between the dark sector and our Standard Model particles are so tiny that they are out of reach of modern experiments, according to Shelton.

    “These ‘nightmare’ scenarios are completely logical possibilities, and in this case, we will have to think very carefully about astrophysical and cosmological ways to look for the footprints of dark particle physics,” she says.

    Even if the dark sector is inaccessible to particle detectors, dark matter will always be visible through the gravitational fingerprint it leaves on the cosmos.

    “Gravity tells us a lot about how much dark matter is in the universe and the kinds of particle interactions dark sector particles can and cannot have,” Shelton says. “For instance, more sensitive gravitational-wave experiments will give us the possibility to look back in time and see what our universe looked like at extremely high energies, and could maybe reveal more about this invisible matter living in our cosmos.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:30 pm on December 31, 2017 Permalink | Reply
    Tags: “The universe is inevitable” he declared. “The universe is impossible.”Nima Arkani-Hamed, CERN LHC, Complications in Physics - "Is Nature Unnatural?", , , Nima Arkani-Hamed of the Institute for Advanced Study, , , , The universe might not make sense   

    From Quanta Magazine: Complications in Physics – “Is Nature Unnatural?” 2013 

    Quanta Magazine
    Quanta Magazine

    May 24, 2013 [Just brought forward in social media.]
    Natalie Wolchover

    Decades of confounding experiments have physicists considering a startling possibility: The universe might not make sense.

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    Is the universe natural or do we live in an atypical bubble in a multiverse? Recent results at the Large Hadron Collider have forced many physicists to confront the latter possibility. Illustration by Giovanni Villadoro.

    On an overcast afternoon in late April, physics professors and students crowded into a wood-paneled lecture hall at Columbia University for a talk by Nima Arkani-Hamed, a high-profile theorist visiting from the Institute for Advanced Study in nearby Princeton, N.J.

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    Nima Arkani-Hamed, Institute for Advanced Study Princeton, N.J., USA
    With his dark, shoulder-length hair shoved behind his ears, Arkani-Hamed laid out the dual, seemingly contradictory implications of recent experimental results at the Large Hadron Collider in Europe.

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    “The universe is impossible,” said Nima Arkani-Hamed, 41, of the Institute for Advanced Study, during a recent talk at Columbia University. Natalie Wolchover/Quanta Magazine

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    “The universe is inevitable,” he declared. “The universe is impossible.”

    The spectacular discovery of the Higgs boson in July 2012 confirmed a nearly 50-year-old theory of how elementary particles acquire mass, which enables them to form big structures such as galaxies and humans.

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    “The fact that it was seen more or less where we expected to find it is a triumph for experiment, it’s a triumph for theory, and it’s an indication that physics works,” Arkani-Hamed told the crowd.

    However, in order for the Higgs boson to make sense with the mass (or equivalent energy) it was determined to have, the LHC needed to find a swarm of other particles, too. None turned up.

    With the discovery of only one particle, the LHC experiments deepened a profound problem in physics that had been brewing for decades. Modern equations seem to capture reality with breathtaking accuracy, correctly predicting the values of many constants of nature and the existence of particles like the Higgs. Yet a few constants — including the mass of the Higgs boson — are exponentially different from what these trusted laws indicate they should be, in ways that would rule out any chance of life, unless the universe is shaped by inexplicable fine-tunings and cancellations.

    In peril is the notion of “naturalness,” Albert Einstein’s dream that the laws of nature are sublimely beautiful, inevitable and self-contained. Without it, physicists face the harsh prospect that those laws are just an arbitrary, messy outcome of random fluctuations in the fabric of space and time.

    The LHC will resume smashing protons in 2015 in a last-ditch search for answers. But in papers, talks and interviews, Arkani-Hamed and many other top physicists are already confronting the possibility that the universe might be unnatural. (There is wide disagreement, however, about what it would take to prove it.)

    “Ten or 20 years ago, I was a firm believer in naturalness,” said Nathan Seiberg, a theoretical physicist at the Institute, where Einstein taught from 1933 until his death in 1955. “Now I’m not so sure. My hope is there’s still something we haven’t thought about, some other mechanism that would explain all these things. But I don’t see what it could be.”

    Physicists reason that if the universe is unnatural, with extremely unlikely fundamental constants that make life possible, then an enormous number of universes must exist for our improbable case to have been realized. Otherwise, why should we be so lucky? Unnaturalness would give a huge lift to the multiverse hypothesis, which holds that our universe is one bubble in an infinite and inaccessible foam. According to a popular but polarizing framework called string theory, the number of possible types of universes that can bubble up in a multiverse is around 10^500. In a few of them, chance cancellations would produce the strange constants we observe.

    In such a picture, not everything about this universe is inevitable, rendering it unpredictable. Edward Witten, a string theorist at the Institute, said by email, “I would be happy personally if the multiverse interpretation is not correct, in part because it potentially limits our ability to understand the laws of physics. But none of us were consulted when the universe was created.”

    “Some people hate it,” said Raphael Bousso, a physicist at the University of California at Berkeley who helped develop the multiverse scenario. “But I just don’t think we can analyze it on an emotional basis. It’s a logical possibility that is increasingly favored in the absence of naturalness at the LHC.”

    What the LHC does or doesn’t discover in its next run is likely to lend support to one of two possibilities: Either we live in an overcomplicated but stand-alone universe, or we inhabit an atypical bubble in a multiverse.

    Multiverse. Image credit: public domain, retrieved from https://pixabay.com/

    “We will be a lot smarter five or 10 years from today because of the LHC,” Seiberg said. “So that’s exciting. This is within reach.

    Cosmic Coincidence

    Einstein once wrote that for a scientist, “religious feeling takes the form of a rapturous amazement at the harmony of natural law” and that “this feeling is the guiding principle of his life and work.” Indeed, throughout the 20th century, the deep-seated belief that the laws of nature are harmonious — a belief in “naturalness” — has proven a reliable guide for discovering truth.

    “Naturalness has a track record,” Arkani-Hamed said in an interview. In practice, it is the requirement that the physical constants (particle masses and other fixed properties of the universe) emerge directly from the laws of physics, rather than resulting from improbable cancellations. Time and again, whenever a constant appeared fine-tuned, as if its initial value had been magically dialed to offset other effects, physicists suspected they were missing something. They would seek and inevitably find some particle or feature that materially dialed the constant, obviating a fine-tuned cancellation.

    This time, the self-healing powers of the universe seem to be failing. The Higgs boson has a mass of 126 giga-electron-volts, but interactions with the other known particles should add about 10,000,000,000,000,000,000 giga-electron-volts to its mass. This implies that the Higgs’ “bare mass,” or starting value before other particles affect it, just so happens to be the negative of that astronomical number, resulting in a near-perfect cancellation that leaves just a hint of Higgs behind: 126 giga-electron-volts.

    Physicists have gone through three generations of particle accelerators searching for new particles, posited by a theory called supersymmetry, that would drive the Higgs mass down exactly as much as the known particles drive it up. But so far they’ve come up empty-handed.

    The upgraded LHC will explore ever-higher energy scales in its next run, but even if new particles are found, they will almost definitely be too heavy to influence the Higgs mass in quite the right way. The Higgs will still seem at least 10 or 100 times too light. Physicists disagree about whether this is acceptable in a natural, stand-alone universe. “Fine-tuned a little — maybe it just happens,” said Lisa Randall, a professor at Harvard University. But in Arkani-Hamed’s opinion, being “a little bit tuned is like being a little bit pregnant. It just doesn’t exist.”

    If no new particles appear and the Higgs remains astronomically fine-tuned, then the multiverse hypothesis will stride into the limelight. “It doesn’t mean it’s right,” said Bousso, a longtime supporter of the multiverse picture, “but it does mean it’s the only game in town.”

    A few physicists — notably Joe Lykken of Fermi National Accelerator Laboratory in Batavia, Ill., and Alessandro Strumia of the University of Pisa in Italy — see a third option. They say that physicists might be misgauging the effects of other particles on the Higgs mass and that when calculated differently, its mass appears natural. This “modified naturalness” falters when additional particles, such as the unknown constituents of dark matter, are included in calculations — but the same unorthodox path could yield other ideas. “I don’t want to advocate, but just to discuss the consequences,” Strumia said during a talk earlier this month at Brookhaven National Laboratory.


    4
    Brookhaven Forum 2013 David Curtin, left, a postdoctoral researcher at Stony Brook University, and Alessandro Strumia, a physicist at the National Institute for Nuclear Physics in Italy, discussing Strumia’s “modified naturalness” idea, which questions longstanding assumptions about how to calculate the natural value of the Higgs boson mass. Thomas Lin/Quanta Magazine.

    However, modified naturalness cannot fix an even bigger naturalness problem that exists in physics: The fact that the cosmos wasn’t instantly annihilated by its own energy the moment after the Big Bang.

    Dark Dilemma

    The energy built into the vacuum of space (known as vacuum energy, dark energy or the cosmological constant) is a baffling trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion times smaller than what is calculated to be its natural, albeit self-destructive, value. No theory exists about what could naturally fix this gargantuan disparity. But it’s clear that the cosmological constant has to be enormously fine-tuned to prevent the universe from rapidly exploding or collapsing to a point. It has to be fine-tuned in order for life to have a chance.

    To explain this absurd bit of luck, the multiverse idea has been growing mainstream in cosmology circles over the past few decades. It got a credibility boost in 1987 when the Nobel Prize-winning physicist Steven Weinberg, now a professor at the University of Texas at Austin, calculated that the cosmological constant of our universe is expected in the multiverse scenario [Physical Review Letters].

    5
    Steven Weinberg, University of Texas at Austin

    Of the possible universes capable of supporting life — the only ones that can be observed and contemplated in the first place — ours is among the least fine-tuned. “If the cosmological constant were much larger than the observed value, say by a factor of 10, then we would have no galaxies,” explained Alexander Vilenkin, a cosmologist and multiverse theorist at Tufts University. “It’s hard to imagine how life might exist in such a universe.”

    Most particle physicists hoped that a more testable explanation for the cosmological constant problem would be found. None has. Now, physicists say, the unnaturalness of the Higgs makes the unnaturalness of the cosmological constant more significant. Arkani-Hamed thinks the issues may even be related. “We don’t have an understanding of a basic extraordinary fact about our universe,” he said. “It is big and has big things in it.”

    The multiverse turned into slightly more than just a hand-waving argument in 2000, when Bousso and Joe Polchinski, a professor of theoretical physics at the University of California at Santa Barbara, found a mechanism that could give rise to a panorama of parallel universes. String theory, a hypothetical “theory of everything” that regards particles as invisibly small vibrating lines, posits that space-time is 10-dimensional. At the human scale, we experience just three dimensions of space and one of time, but string theorists argue that six extra dimensions are tightly knotted at every point in the fabric of our 4-D reality. Bousso and Polchinski calculated that there are around 10500 different ways for those six dimensions to be knotted (all tying up varying amounts of energy), making an inconceivably vast and diverse array of universes possible. In other words, naturalness is not required. There isn’t a single, inevitable, perfect universe.

    “It was definitely an aha-moment for me,” Bousso said. But the paper sparked outrage.

    “Particle physicists, especially string theorists, had this dream of predicting uniquely all the constants of nature,” Bousso explained. “Everything would just come out of math and pi and twos. And we came in and said, ‘Look, it’s not going to happen, and there’s a reason it’s not going to happen. We’re thinking about this in totally the wrong way.’ ”

    Life in a Multiverse

    The Big Bang, in the Bousso-Polchinski multiverse scenario, is a fluctuation. A compact, six-dimensional knot that makes up one stitch in the fabric of reality suddenly shape-shifts, releasing energy that forms a bubble of space and time. The properties of this new universe are determined by chance: the amount of energy unleashed during the fluctuation. The vast majority of universes that burst into being in this way are thick with vacuum energy; they either expand or collapse so quickly that life cannot arise in them. But some atypical universes, in which an improbable cancellation yields a tiny value for the cosmological constant, are much like ours.

    In a paper posted last month to the physics preprint website arXiv.org, Bousso and a Berkeley colleague, Lawrence Hall, argue that the Higgs mass makes sense in the multiverse scenario, too. They found that bubble universes that contain enough visible matter (compared to dark matter) to support life most often have supersymmetric particles beyond the energy range of the LHC, and a fine-tuned Higgs boson. Similarly, other physicists showed in 1997 that if the Higgs boson were five times heavier than it is, this would suppress the formation of atoms other than hydrogen, resulting, by yet another means, in a lifeless universe.

    Despite these seemingly successful explanations, many physicists worry that there is little to be gained by adopting the multiverse worldview. Parallel universes cannot be tested for; worse, an unnatural universe resists understanding. “Without naturalness, we will lose the motivation to look for new physics,” said Kfir Blum, a physicist at the Institute for Advanced Study. “We know it’s there, but there is no robust argument for why we should find it.” That sentiment is echoed again and again: “I would prefer the universe to be natural,” Randall said.

    But theories can grow on physicists. After spending more than a decade acclimating himself to the multiverse, Arkani-Hamed now finds it plausible — and a viable route to understanding the ways of our world. “The wonderful point, as far as I’m concerned, is basically any result at the LHC will steer us with different degrees of force down one of these divergent paths,” he said. “This kind of choice is a very, very big deal.”

    Naturalness could pull through. Or it could be a false hope in a strange but comfortable pocket of the multiverse.

    As Arkani-Hamed told the audience at Columbia, “stay tuned.”

    See the full article here .

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 2:56 pm on December 23, 2017 Permalink | Reply
    Tags: ADMX Axion Dark Matter Experiment at the University of Washington, , CERN LHC, Cosmic Axion Spin-Precession Experiment (CASPEr), , International Linear Collider in Japan, Large Underground Xenon (LUX) dark matter experiment, LBNL LZ project at SURF Lead SD USA, MACHOs, SIMPs, ,   

    From UC Berkeley: “MACHOs are Dead. WIMPs are a No-Show. Say Hello to SIMPs” 

    UC Berkeley

    UC Berkeley

    December 4, 2017
    Robert Sanders
    rlsanders@berkeley.edu

    The intensive, worldwide search for dark matter, the missing mass in the universe, has so far failed to find an abundance of dark, massive stars or scads of strange new weakly interacting particles, but a new candidate is slowly gaining followers and observational support.

    1
    Fundamental structures of a pion (left) and a proposed SIMP (strongly interacting massive particle). Pions are composed of an up quark and a down antiquark, with a gluon (g) holding them together. A SIMP would be composed of a quark and an antiquark held together by an unknown type of gluon (G). (Kavli IPMU graphic)

    Called SIMPs – strongly interacting massive particles – they were proposed three years ago by UC Berkeley theoretical physicist Hitoshi Murayama, a professor of physics and director of the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) in Japan, and former UC Berkeley postdoc Yonit Hochberg, now at Hebrew University in Israel.

    Murayama says that recent observations of a nearby galactic pile-up [Nature] could be evidence for the existence of SIMPs, and he anticipates that future particle physics experiments will discover one of them.

    Murayama discussed his latest theoretical ideas about SIMPs and how the colliding galaxies support the theory in an invited talk Dec. 4 at the 29th Texas Symposium on Relativistic Astrophysics in Cape Town, South Africa.

    Astronomers have calculated that dark matter, while invisible, makes up about 85 percent of the mass of the universe. The solidest evidence for its existence is the motion of stars inside galaxies: Without an unseen blob of dark matter, galaxies would fly apart. In some galaxies, the visible stars are so rare that dark matter makes up 99.9 percent of the mass of the galaxy.

    Theorists first thought that this invisible matter was just normal matter too dim to see: failed stars called brown dwarfs, burned-out stars or black holes. Yet so-called massive compact halo objects – MACHOs – eluded discovery, and earlier this year a survey of the Andromeda galaxy by the Subaru Telescope basically ruled out any significant undiscovered population of black holes.


    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA,4,207 m (13,802 ft) above sea level

    The researchers searched for black holes left over from the very early universe, so-called primordial black holes, by looking for sudden brightenings produced when they pass in front of background stars and act like a weak lens. They found exactly one – too few to contribute significantly to the mass of the galaxy.

    3
    This Hubble Space Telescope image of the galaxy cluster Abell 3827 shows the ongoing collision of four bright galaxies and one faint central galaxy, as well as foreground stars in our Milky Way galaxy and galaxies behind the cluster (Arc B and Lensed image A) that are distorted because of normal and dark matter within the cluster. SIMPs could explain why the dark matter, unseen but detectable because of the lensing, lags behind the normal matter in the collision.

    “That study pretty much eliminated the possibility of MACHOs; I would say it is pretty much gone,” Murayama said.

    WIMPs — weakly interacting massive particles — have fared no better, despite being the focus of researchers’ attention for several decades. They should be relatively large – about 100 times heavier than the proton – and interact so rarely with one another that they are termed “weakly” interacting. They were thought to interact more frequently with normal matter through gravity, helping to attract normal matter into clumps that grow into galaxies and eventually spawn stars.

    SIMPs interact with themselves, but not others.

    SIMPs, like WIMPs and MACHOs, theoretically would have been produced in large quantities early in the history of the universe and since have cooled to the average cosmic temperature. But unlike WIMPs, SIMPs are theorized to interact strongly with themselves via gravity but very weakly with normal matter. One possibility proposed by Murayama is that a SIMP is a new combination of quarks, which are the fundamental components of particles like the proton and neutron, called baryons. Whereas protons and neutrons are composed of three quarks, a SIMP would be more like a pion in containing only two: a quark and an antiquark.

    4
    Conventional WIMP theories predict that dark matter particles rarely interact. Murayama and Hochberg predict that dark matter SIMPs, comprised of a quark and an antiquark, would collide and interact, producing noticeable effects when the dark matter in galaxies collide. (Kavli IPMU graphic)

    The SIMP would be smaller than a WIMP, with a size or cross section like that of an atomic nucleus, which implies there are more of them than there would be WIMPs. Larger numbers would mean that, despite their weak interaction with normal matter – primarily by scattering off of it, as opposed to merging with or decaying into normal matter – they would still leave a fingerprint on normal matter, Murayama said.

    He sees such a fingerprint in four colliding galaxies within the Abell 3827 cluster, where, surprisingly, the dark matter appears to lag behind the visible matter. This could be explained, he said, by interactions between the dark matter in each galaxy that slows down the merger of dark matter but not that of normal matter, basically stars.

    “One way to understand why the dark matter is lagging behind the luminous matter is that the dark matter particles actually have finite size, they scatter against each other, so when they want to move toward the rest of the system they get pushed back,” Murayama said. “This would explain the observation. That is the kind of thing predicted by my theory of dark matter being a bound state of new kind of quarks.”

    SIMPs also overcome a major failing of WIMP theory: the ability to explain the distribution of dark matter in small galaxies.

    5
    Conventional WIMP theories predict a highly peaked distribution, or cusp, of dark matter in a small area in the center of every galaxy. SIMP theory predicts a spread of dark matter in the center, which is more typical of dwarf galaxies. (Kavli IPMU graphic based on NASA, STScI images)

    “There has been this longstanding puzzle: If you look at dwarf galaxies, which are very small with rather few stars, they are really dominated by dark matter. And if you go through numerical simulations of how dark matter clumps together, they always predict that there is a huge concentration towards the center. A cusp,” Murayama said. “But observations seem to suggest that concentration is flatter: a core instead of a cusp. The core/cusp problem has been considered one of the major issues with dark matter that doesn’t interact other than by gravity. But if dark matter has a finite size, like a SIMP, the particles can go ‘clink’ and disperse themselves, and that would actually flatten out the mass profile toward the center. That is another piece of ‘evidence’ for this kind of theoretical idea.”

    Ongoing searches for WIMPs and axions

    Ground-based experiments to look for SIMPs are being planned, mostly at accelerators like the Large Hadron Collider at CERN in Geneva, where physicists are always looking for unknown particles that fit new predictions.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Another experiment at the planned International Linear Collider in Japan could also be used to look for SIMPs.

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

    As Murayama and his colleagues refine the theory of SIMPs and look for ways to find them, the search for WIMPs continues. The Large Underground Xenon (LUX) dark matter experiment in an underground mine in South Dakota has set stringent limits on what a WIMP can look like, and an upgraded experiment called LZ will push those limits further. Daniel McKinsey, a UC Berkeley professor of physics, is one of the co-spokespersons for this experiment, working closely with Lawrence Berkeley National Laboratory, where Murayama is a faculty senior scientist.

    Lux Dark Matter 2 at SURF, Lead, SD, USA

    LBNL LZ project at SURF, Lead, SD, USA

    Physicists are also seeking other dark matter candidates that are not WIMPs. UC Berkeley faculty are involved in two experiments looking for a hypothetical particle called an axion, which may fit the requirements for dark matter. The Cosmic Axion Spin-Precession Experiment (CASPEr), led by Dmitry Budker, a professor emeritus of physics who is now at the University of Mainz in Germany, and theoretician Surjeet Rajendran, a UC Berkeley professor of physics, is planning to look for perturbations in nuclear spin caused by an axion field. Karl van Bibber, a professor of nuclear engineering, plays a key role in the (ADMX-HF), which seeks to detect axions inside a microwave cavity within a strong magnetic field as they convert to photons.

    ADMX Axion Dark Matter Experiment at the University of Washington

    “Of course we shouldn’t abandon looking for WIMPs,” Murayama said, “but the experimental limits are getting really, really important. Once you get to the level of measurement, where we will be in the near future, even neutrinos end up being the background to the experiment, which is unimaginable.”

    Neutrinos interact so rarely with normal matter that an estimated 100 trillion fly through our bodies every second without our noticing, something that makes them extremely difficult to detect.

    “The community consensus is kind of, we don’t know how far we need to go, but at least we need to get down to this level,” he added. “But because there are definitely no signs of WIMPs appearing, people are starting to think more broadly these days. Let’s stop and think about it again.”

    Murayama’s research is supported by the U.S. Department of Energy, National Science Foundation and Japanese Ministry of Education, Culture, Sports, Science and Technology. Murayama is also collaborating with Eric Kuflik of Hebrew University, Tomer Volansky of Tel Aviv University and Jay Wacker of Quora Inc. in Mountain View, California, and Stanford University.

    See the full article here .

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  • richardmitnick 1:08 pm on December 15, 2017 Permalink | Reply
    Tags: , , , CERN LHC, , , , Plotting the Phase Transitions, , Recreating the Beginning of the Universe   

    From BNL: “How to Map the Phases of the Hottest Substance in the Universe” 

    Brookhaven Lab

    December 11, 2017
    Shannon Brescher Shea

    Scientists are searching for the critical point of quark-gluon plasma, the substance that formed just after the Big Bang. Finding where quark-gluon plasma abruptly changes into ordinary matter can reveal new insights.

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    The universe began as a fireball 250,000 times hotter than the core of the sun. Just microseconds after the Big Bang, the protons and neutrons that make up the building blocks of nuclei, the heart of atoms, hadn’t yet formed. Instead, we had the quark-gluon plasma, a blazing 4 trillion degree Celsius liquid of quarks, gluons, and other particles such as electrons. At that very earliest moment, it was as if the entire universe was a tremendous, churning lake of gluon “water” filled with quark “pebbles.”

    In less than a heartbeat, the universe cooled, “freezing” the lake. Instead of becoming a solid block, everything separated out into clusters of quark “pebbles” connected by gluon “ice.” When some of these quarks joined together, they became our familiar protons and neutrons. After a few minutes, those protons and neutrons came together to form nuclei, which make up the cores of atoms. Quarks and gluons are two of the most basic subatomic particles in existence. Today, quarks make up protons and neutrons while gluons hold the quarks together.

    But since the Big Bang, quarks and gluons have never appeared by themselves in ordinary matter. They’re always found within protons or neutrons.

    Except for a few very special places in the world. In facilities supported by the Department of Energy’s (DOE) Office of Science, scientists are crashing gold ions into each other to recreate quark-gluon plasma. They’re working to map how and when quark-gluon plasma transforms into ordinary matter. Specifically, they’re looking for the critical point – that strange and precise place that marks a change from one type of transition to another between quark-gluon plasma and our familiar protons and neutrons.

    Recreating the Beginning of the Universe

    Because quark-gluon plasma could provide insight into universe’s origins, scientists have wanted to understand it for decades. It could help scientists better comprehend how today’s complex matter arises from the relatively straightforward laws of physics.

    But scientists weren’t able to study quark-gluon plasma experimentally at high energies until 2000. That’s when researchers at DOE’s Brookhaven National Laboratory flipped the switch on the Relativistic Heavy Ion Collider (RHIC), an Office of Science user facility. This particle accelerator was the first to collide beams of heavy ions (heavy atoms with their electrons stripped off) head-on into each other.

    It all starts with colliding ions made of protons and neutrons into each other. The bunches of ions smash together and create about a hundred thousand collisions a second. When the nuclei of the ions first collide, quarks and gluons break off and scatter. RHIC’s detectors identify and analyze these particles to help scientists understand what is happening inside the collisions.

    As the collision reaches temperatures hot enough to melt protons and neutrons, the quark-gluon plasma forms and then expands. When the collisions between nuclei aren’t perfectly head-on, the plasma flows in an elliptical pattern with almost zero resistance. It actually moves 10 billion trillion times fasterExternal link than the most powerful tornado. The quarks in it strongly interact, with many particles constantly bouncing off their many neighbors and passing gluons back and forth. If the universe began in a roiling quark-gluon lake, inside the RHIC is a miniscule but ferocious puddle.

    Then, everything cools down. The quarks and gluons cluster into protons, neutrons, and other subatomic particles, no longer free.

    All of this happens in a billionth of a trillionth of a second.

    After running these experiments for years, scientists at RHIC finally found what they were looking for. The data from billions of collisions gave them enough evidence to declare that they had created quark-gluon plasma. Through temperature measurements, they could definitively say the collisions created by RHIC were hot enough to melt protons and neutrons, breaking apart the quark-gluon clusters into something resembling the plasma at the very start of the universe.

    Since then, scientists at the Large Hadron Collider at CERN in Geneva have also produced quark-gluon plasma.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Researchers at both facilities are working to better understand this strange form of matter and its phases.

    Plotting the Phase Transitions.

    2
    This diagram plots out what scientists theorize about quark-gluon plasma’s phases using the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). Baryon density is the density of the particles in the matter.

    All matter has different phases. A phase is a form where matter has consistent physical properties, such as density, magnetism, and electrical conductivity. The best-known phases are solid, liquid, and gas. For example, water’s conventional phases are ice, liquid water, and steam. Beyond the phases familiar to us, there’s also the plasma phase that makes up stars and the utterly unique quark-gluon plasma.

    Phase transitions, where materials move between phases, reveal a great deal about how matter functions. Materials usually change phases because they experience a change in temperature or pressure.

    “Phase transitions are an amazing phenomenon in nature,” said Jamie Nagle, a professor at the University of Colorado at Boulder who conducts research at RHIC. “Something that molecularly is the same can look and behave in a dramatically different way.”

    Like many types of matter, quark-gluon plasma goes through phase transitions. But because quarks and gluons haven’t existed freely in ordinary matter since the dawn of time, it acts differently than what we’re used to.

    In most circumstances, matter goes through first-order phase transitions. These changes result in major shifts in density, such as from liquid water to ice. These transitions also use or release a lot of heat. Water freezing into ice releases energy; ice melting into water absorbs energy.

    But quark-gluon plasma is different. In quark-gluon plasma, scientists haven’t seen the first-order phase transition. They’ve only seen what they call smooth or continuous cross-over transformations. In this state, gluons move back and forth smoothly between being free and trapped in protons and neutrons. Their properties are changing so often that it’s difficult to distinguish between the plasma and the cloud of ordinary matter. This phase can also happen in ordinary matter, but usually under extreme circumstances. For example, if you boil water at 217 times the pressure of our atmosphere, it’s nearly impossible to tell the difference between the steam and liquid.

    Even though scientists haven’t seen the first-order phase transition yet, the physics theory that describes quark-gluon plasma predicts there should be one. The theory also predicts a particular critical point, where the first-order phase transition ends.

    “This is really the landmark that we’re looking for,” said Krishna Rajagopal, a theoretical physicist and professor at the Massachusetts Institute of Technology (MIT).

    Understanding the relationships between these phases could provide insight into phenomena beyond quark-gluon plasma. In fact, scientists have applied what they’ve learned from studying quark-gluon plasma to better understand superconductors. Scientists can also use this knowledge to understand other places where plasma may occur in the universe, such as stars.

    As John Harris, a Yale University professor, said, “How do stars, for example, evolve? Are there such stars out there that have quark-gluon cores? Could neutron-star mergers go through an evolution that includes quark-gluon plasma in their final moments before they form black holes?”

    The Search Continues

    These collisions have allowed scientists to sketch out the basics of quark-gluon plasma’s phases. So far, they’ve seen that ordinary matter occurs at the temperatures and densities that we find in most of the universe. In contrast, quark-gluon plasma occurs at extraordinarily high temperatures and densities. While scientists haven’t been able to produce the right conditions, theory predicts that quark-gluon plasma or an even more exotic form of matter may occur at low temperatures with very high densities. These conditions could occur in neutron stars, which weigh 10 billion tons per cubic inch.

    Delving deeper into these phases will require physicists to draw from both theory and experimental data.

    Theoretical physics predicts the critical point exists somewhere under conditions that are at lower temperatures and higher densities than RHIC can currently reach. But scientists can’t use theory alone to predict the exact temperature and density where it would occur.

    “Different calculations that do things a bit differently give different predictions,” said Barbara Jacak, the director of the Nuclear Science division at DOE’s Lawrence Berkeley National Laboratory. “So I say, ‘Aha, experiment to the rescue!'”

    What theory can do is provide hints as to what to look for in experiments. Some collisions near the critical point should produce first-order transitions, while others produce smooth cross-over ones. Because each type of phase transition produces different types and numbers of particles, the collisions should, too. As a result, scientists should see large variations in the numbers and types of particles created from collision to collision near the critical point. There may also be big fluctuations in electric charge and other types of phenomena.

    The only way to see these transitions is to collide particles at a wide range of energies. RHIC is the only machine in the world that can do this. While the Large Hadron Collider can produce quark-gluon plasma, it can’t collide heavy ions at low enough energy levels to find the critical point.

    So far, scientists have done an initial “energy scan” where they have run RHIC at a number of different energy levels. However, RHIC’s current capabilities limit the data they’ve been able to collect.

    “We had some very intriguing results, but nothing that was so statistically significant that you could declare victory,” said Rosi Reed, a Lehigh University assistant professor who conducts research at RHIC.

    RHIC is undergoing upgrades to its detector that will vastly increase the number of collisions scientists can study. It will also improve how accurately they can study them. When RHIC relaunches, scientists envision these hints turning into more definitive answers.

    From milliseconds after the Big Bang until now, the blazing lake of quark-gluon plasma has only existed for the smallest fraction of time. But it’s had an outsized influence on everything we see.

    As Gene Van Buren, a scientist at DOE’s Brookhaven National Laboratory, said, “We’re making stuff in the laboratory that no one else has really had the chance to do in human history.”

    See the full article here .

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    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.
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  • richardmitnick 2:12 pm on November 28, 2017 Permalink | Reply
    Tags: , CERN LHC, , Protons,   

    From Symmetry: “LHC data: how it’s made” 

    Symmetry Mag
    Symmetry

    11/28/17
    Sarah Charley

    1
    Photo by Silvia Biondi; Matteo Franchini, CERN

    In the Large Hadron Collider, protons become new particles, which become energy and light, which become data.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Scientists have never actually seen the Higgs boson.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    They’ve never seen the inside of a proton, either, and they’ll almost certainly never see dark matter. Many of the fundamental patterns woven into the fabric of nature are completely imperceptible to our clunky human senses.

    But scientists don’t need to see particles to learn about their properties and interactions. Physicists can study the subatomic world with particle detectors, which gather information from events that occur much faster and are much smaller than the eye can see.

    But what is this information, and how exactly do detectors gather it? At experiments at the Large Hadron Collider, the world’s largest and most powerful particle accelerator, it all begins with a near-light-speed race.

    Starting with a bang

    The LHC is built in a ring 17 miles in circumference. Scientists load bunches of protons into this ring and send them hurtling around in opposite directions, gaining more and more energy with each pass.

    By the time the LHC has boosted the proton beams to their maximum energy, they will have traveled a distance equivalent to a round-trip journey between Earth and the sun. They will be moving so fast that they no longer convert energy into speed but in effect swell with mass instead.

    Once the protons are ramped up to their final energy, the LHC’s magnets nudge the two beams into a collision course at four intersections around the ring.

    CERN/ATLAS detector

    CERN/CMS Detector

    CERN/LHCb detector

    CERN ALICE detector

    “When two protons traveling at near light speeds collide head-on, the impact releases a surge of energy unimaginably quickly in an unimaginably small volume of space,” says Dhiman Chakraborty, a professor of Physics at Northern Illinois University working on the ATLAS experiment. “In that miniscule volume, conditions are similar to those that prevailed when the universe was a mere tenth of a nanosecond old.”

    This energy is often converted directly into mass according to Einstein’s famous equation, E=mc2, resulting in birth of exotic particles not to be found anywhere else on Earth. These particles, which can include Higgs bosons, are extremely short-lived.

    “They decay instantaneously and spontaneously into less massive, more stable ‘daughter’ particles,” Chakraborty says. “The large mass of the exotic parent particle, being converted back into energy, sends its much lighter daughters flying off at near light speeds.”

    Even though these rare particles are short-lived, they give scientists a peek at the texture of spacetime and the ubiquitous fields woven into it.

    “So much so that the existence of the entire universe we see today—ourselves as observers included—is owed to [the particles and fields we cannot see],” he says.

    3
    This CMS experiment event display identifies an electron and a muon passing through the detector. Courtesy of CMS Collaboration

    Enter the detector

    All of this happens in less than a millionth of a trillionth of a second. Even though the LHC’s detectors encompass the beampipe and are only a few centimeters away from the collison, it is impossible for them to see the new heavy particles, which often disintegrate before they can move a distance equal to the diameter of an atomic nucleus.

    But the detectors can “see” the byproducts of their decay. The Higgs bosons can transform into pairs of photons, for example. When those photons hit the atoms and molecules that make up the detector material, they radiate sparkles of light and jolts of energy like meteorites blazing through the atmosphere. Sensors inhale these dim twinkles and transform them into electrical signals, recording where and when they arrived.

    “Each pulse is a snapshot of space and time,” Chakraborty says. “They tell us exactly where, when and how fast those daughter particles traversed our detector.”

    A single proton-proton collision can generate several high-energy daughter particles, some of which produce showers of hundreds more. These streams of particles release detectable energy as they hit the detectors and generate electrical pulses. The time, location, length, shape, height and total energy of each electrical pulse are directly translated into data bits by an electronic readout card.

    Much the way biologists chart animal tracks to study the speed, direction and size of a herd, physicists study the shape of these electrical pulses to characterize the passing particles. A long, broad electrical pulse indicates that a large stream of particles grazed across the detector, but a pulse with a sharp peak suggests that a small pack cut straight through.

    These electrical pulses create a multifaceted connect-the-dots. Algorithms quickly identify patterns in the cascade of hits and rapidly reconstruct particle energies and tracks.

    “We only have a few microseconds to reconstruct what happened before the next batch of collisions arrives,” says Tulika Bose, an associate professor at Boston University working on the CMS experiment. “We can’t keep all the data, so we use automated systems to crudely reconstruct particles like muons and electrons.

    “If the event looks interesting enough based on this limited amount of information, we keep all the data from that snapshot in time and save them for further analysis.”

    These interesting events are packaged and dispatched upstairs to a second series of automated gatekeepers that further evaluate the quality and characteristics of these collision snapshots. Preprogrammed algorithms identify more particles in the snapshot. This entire process takes less than a millisecond, faster than the blink of a human eye.

    Even then, humans won’t lay eyes on the data until after it undergoes a strenuous suite of processing and preparation for analysis.

    Humans can’t see the Higgs boson, but by tracing its byproducts back to a single Higgs-like origin, they were able to gather enough evidence to discover it.

    “In the five years since that discovery, we’ve produced hundreds of thousands more Higgs bosons and reconstructed a good number of them,” Chakraborty says. “They’re being studied intensely with the goal of gaining insight into deeper mysteries of nature.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:53 am on November 22, 2017 Permalink | Reply
    Tags: , , CERN LHC, , , , , ,   

    From Futurism: “Quantum Physicists Conclude Necessary Makeup of Elusive Tetraquarks” 

    futurism-bloc

    Futurism

    Mesons Baryons Tetraquarks

    , https://blog.cerebrodigital.org/tetraquark-particula-exotica-descubierta-en-fermilab/

    November 20, 2017
    Abby Norman

    Everything in the universe is made up of atoms — except, of course, atoms themselves. They’re made up of subatomic particles, namely, protons, neutrons, and electrons. While electrons are classified as leptons, protons and neutrons are in a class of particles known as quarks. Though, “known” may be a bit misleading: there is a lot more theoretical physicists don’t know about the particles than they do with any degree of certainty.

    As far as we know, quarks are the fundamental particle of the universe. You can’t break a quark down into any smaller particles. Imagining them as being uniformly minuscule is not quite accurate, however: while they are tiny, they are not all the same size. Some quarks are larger than others, and they can also join together and create mesons (1 quark + 1 antiquark) or baryons (3 quarks of various flavors).

    In terms of possible quark flavors, which are respective to their position, we’ve identified six: up, down, top, bottom, charm, and strange. As mentioned, they usually pair up either in quark-antiquark pairs or a quark threesome — so long as the charges ( ⅔, ⅔, and ⅓ ) all add up to positive 1.

    The so-called tetraquark pairing has long-eluded scientists; a hadron which would require 2 quark-antiquark pairs, held together by the strong force. Now, it’s not enough for them to simply pair off and only interact with their partner. To be a true tetraquark, all four quarks would need to interact with one another; behaving as quantum swingers, if you will.

    “Quarky” Swingers

    It might seem like a pretty straightforward concept: throw four quarks together and they’re bound to interact, right? Well, not necessarily. And that would be assuming they’d pair off stably in the first place, which isn’t a given. As Marek Karliner of Tel Aviv University explained to LiveScience, two quarks aren’t any more likely to pair off in a stable union than two random people you throw into an apartment together. When it comes to both people and quarks, close proximity doesn’t ensure chemistry.

    “The big open question had been whether such combinations would be stable,
    or would they instantly disintegrate into two quark-antiquark mesons,” Karliner told Futurism. “Many years of experimental searches came up empty-handed, and no one knew for sure whether stable tetraquarks exist.”

    Most discussions of tetraquarks up until recently involved those “ad-hoc” tetraquarks; the ones where four quarks were paired off, but not interacting. Finding the bona-fide quark clique has been the “holy grail” of theoretical physics for years – and we’re agonizingly close.

    Recalling that quarks are not something we can actually see, it probably goes without saying that predicting the existence of such an arrangement would be incredibly hard to do. The very laws of physics dictate that it would be impossible for four quarks to come together and form a stable hadron. But two physicists found a way to simplify (as much as you can “simplify” quantum mechanics) the approach to the search for tetraquarks.

    Several years ago, Karliner and his research partner, Jonathan Rosner of the University of Chicago, set out to establish the theory that if you want to know the mass and binding energy of rare hadrons, you can start by comparing them to the common hadrons you already know the measurements for. In their research [Nature] they looked at charm quarks; the measurements for which are known and understood (to quantum physicists, at least).

    Based on these comparisons, they proposed that a doubly-charged baryon should have a mass of 3,627 MeV, +/- 12 MeV [Physical Review Letters]. The next step was to convince CERN to go tetraquark-hunting, using their math as a map.

    For all the complex work it undertakes, the vast majority of which is nothing detectable by the human eye, The Large Hadron Collider is exactly what the name implies: it’s a massive particle accelerator that smashes atoms together, revealing their inner quarks.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    If you’re out to prove the existence of a very tiny theoretical particle, the LHC is where you want to start — though there’s no way to know how long it will be before, if ever, the particles you seek appear.

    It took several years, but in the summer of 2017, the LHC detected a new baryon: one with a single up quark and two heavy charm quarks — the kind of doubly-charged baryon Karliner and Rosner were hoping for. The mass of the baryon was 3,621 MeV, give or take 1 MeV, which was extremely close to the measurement Karliner and Rosner had predicted. Prior to this observation physicists had speculated about — but never detected — more than one heavy quark in a baryon. In terms of the hunt for the tetraquark, this was an important piece of evidence: that more robust bottom quark could be just what a baryon needs to form a stable tetraquark.

    The perpetual frustration of studying particles is that they don’t stay around long. These baryons, in particular, disappear faster than “blink-and-you’ll-miss-it” speed; one 10/trillionth of a second, to be exact. Of course, in the world of quantum physics, that’s actually plenty of time to establish existence, thanks to the LHC.

    The great quantum qualm within the LHC, however, is one that presents a significant challenge in the search for tetraquarks: heavier particles are less likely to show up, and while this is all happening on an infinitesimal level, as far as the quantum scale is concerned, bottom quarks are behemoths.

    The next question for Rosner and Karliner, then, was did it make more sense to try to build a tetraquark, rather than wait around for one to show up? You’d need to generate two bottom quarks close enough together that they’d hook up, then throw in a pair of lighter antiquarks — then do it again and again, successfully, enough times to satisfy the scientific method.

    “Our paper uses the data from recently discovered double-charmed baryon to point, for the first time, that a stable tetraquark *must* exist,” Karliner told Futurism, adding that there’s “a very good chance” the LHCb at CERN would succeed in observing the phenomenon experimentally.

    That, of course, is still a theoretical proposition, but should anyone undertake it, the LHC would keep on smashing in the meantime — and perhaps the combination would arise on its own. As Karliner reminded LiveScience, for years the assumption has been that tetraquarks are impossible. At the very least, they’re profoundly at odds with the Standard Model of Physics. But that assumption is certainly being challenged. “The tetraquark is a truly new form of strongly-interacting matter,” Karliner told Futurism,” in addition to ordinary baryons and mesons.”

    If tetraquarks are not impossible, or even particularly improbable, thanks to the Karliner and Rosner’s calculations, at least now we have a better sense of what we’re looking for — and where it might pop up.

    Where there’s smoke there’s fire, as they say, and while the mind-boggling realm of quantum mechanics may feel more like smoke and mirrors to us, theoretical physicists aren’t giving up just yet. Where there’s a 2-bottom quark, there could be tetraquarks.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Futurism covers the breakthrough technologies and scientific discoveries that will shape humanity’s future. Our mission is to empower our readers and drive the development of these transformative technologies towards maximizing human potential.

     
  • richardmitnick 3:22 pm on November 21, 2017 Permalink | Reply
    Tags: , , , CERN LHC, , , , , , , ,   

    From Symmetry: “Putting the puzzle together” 

    Symmetry Mag
    Symmetry

    11/21/17
    Ali Sundermier

    1
    Photos by Fermilab and CERN

    Successful physics collaborations rely on cooperation between people from many different disciplines.

    So, you want to start a physics experiment. Maybe you want to follow hints of an as yet unseen particle. Or maybe you want to learn something new about a mysterious process in the universe. Either way, your next step is to find people who can help you.

    In large science collaborations, such as the ATLAS and CMS experiments at the Large Hadron Collider; the Deep Underground Neutrino Experiment (DUNE); and Fermilab’s NOvA, hundreds to thousands of people spread out across many institutions and countries keep things operating smoothly. Whether they’re senior scientists, engineers, technicians or administrators, each of them has an important role to play.

    CERN/ATLAS detector

    CERN/CMS Detector

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

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


    FNAL DUNE Argon tank at SURF


    Surf-Dune/LBNF Caverns at Sanford



    SURF building in Lead SD USA

    FNAL NOvA Near Detector


    FNAL/NOvA experiment map

    Think of it like a jigsaw puzzle: This list will give you an idea about how their work fits together to create the big picture.

    Dreaming up the experiment

    Many particle physics experiments begin with a fundamental question. Why do objects have mass? Or, why is the universe made of matter?

    When scientists encounter these big, seemingly inscrutable questions, part of their job is to identify possible ways to answer them. A large part of this is breaking down the big questions into a program of smaller, answerable questions.

    In the case of the LHC, scientists who wondered about things such as undiscovered particles and the origin of mass designed a 27-kilometer particle collider and four giant detectors to learn more.

    Each scientist in a collaboration brings their own unique perspective and skill set to the table, whether it’s providing an understanding of the physics or offering expertise in operations or detector design.

    Perfecting the design

    Once scientists have an idea about the experiment they want to do and the approach they want to take, it’s the job of the engineers to turn the concepts into pieces of hardware that can be built, function and meet the experiment’s requirements.

    For example, engineers might have to figure out how the experiment should be supported mechanically or how to connect all the electrical systems and make signals available in a detector.

    In the case of NOvA, which investigates neutrino oscillations, scientists needed a detector that was huge and free of dense materials, which made conventional construction techniques unworkable. They had to work with engineers who could understand plastic as a building material so they could be confident about using it to build a gigantic, free-standing structure that fit the requirements.

    Keeping things running

    Technicians come in when the experimental apparatus and instrumentation are being built and often have complementary knowledge about what they’re working on. They build the hardware and coordinate the integration of components. It’s their work that, in the end, pulls everything together so the experiment functions.

    Once the experiment is built, technicians are responsible for keeping everything humming along at top performance. When physicists notice things going wrong with the detectors, the technicians usually have first eyes on it. It’s a vital task, since every second counts when it comes to collecting data.

    Doing the heavy lifting

    When designing and constructing the experiment, the scientists also recruit postdocs and grad students, who do the bulk of the data analysis.

    Grad students, who are still working on their PhDs, have to balance their own coursework with the real-world experiment, learning their way around running simulations, analyzing data and developing algorithms. They also make sure that every part of the detector is working up to par. In addition, they may work in instrumentation, developing new instruments and electronics.

    Postdocs, on the other hand, have already worked on experiments and obtained their PhDs, so they typically assume more of a leadership role in these collaborations. Part of their role is to guide the grad students in a sort of apprenticeship.

    Postdocs are often in charge of certain types of analysis or detector operations. Because they’ve worked on previous experiments, they have a tool kit and experience to draw on to solve problems when they crop up.

    Postdocs and grad students often work with technicians and engineers to ensure everything is properly built.

    Making the data accessible

    The LHC produces about 25 petabytes of data every year, or 25 billion megabytes. If the average size of an MP3 is about one megabyte per minute, then it would take almost 50,000 years to play 25 petabytes of songs. In physics collaborations, computer scientists and engineers have to organize the computing networks to ensure against bottlenecks or traffic jams when this massive amount of data is shared.

    They also maintain the software framework, which takes care of data handling and archiving. Say a scientist wants to know what happened on Feb. 27, 2015, at 3 a.m. Computing experts have to be able to go into the data catalogue and find, among the petabytes of data, where that event is stored.

    Sorting out the logistics

    One often overlooked group is the administrators.

    It’s up to the administrators to sequence all the different projects so they get the funds they need to make progress. They sort the logistics to make sure the right people are in the right places working on the right things.

    Administrators manage a group of people who are constantly coming and going. Is someone traveling to a site from a different institution? The administrators make sure that people get connected, work out itineraries and schedule where visiting scientists will live and work.

    Administrators also organize collaboration meetings, transfer money, and procure and ship equipment.

    Translating discoveries to the public

    While every single person involved in an experiment has a responsibility to effectively communicate with others, it can be challenging to communicate about research in a way that’s relatable to people from different backgrounds. That’s where the professional communicators come in.

    Communicators can translate a paper full of jargon and complicated science into a fascinating story that the rest of the world can get excited about.

    In addition to doing outreach for the public and writing press releases and pitching stories for the media, communicators offer coaching to people in a scientific collaboration on how to relay the science to a general audience, which is important for generating public interest.

    Fitting the pieces

    Now that you know many of the pieces that must fall into place for a large physics collaboration to be successful, also know that none of these roles is performed in a vacuum. For an experiment to work, there must be a synergy of tasks: Each relies on the success of the others. Now go start that experiment!

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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