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

    From CERN: “Long-lived physics” 

    Cern New Bloc

    Cern New Particle Event

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    CERN

    18 Jan 2018
    Iva Raynova

    1
    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.

    1

    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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  • richardmitnick 12:16 pm on January 18, 2018 Permalink | Reply
    Tags: , , , HEP, Measurements of weak top quark processes gain strength, ,   

    From ATLAS at CERN: “Measurements of weak top quark processes gain strength” 

    This post is dedicated to L.Z. from H.P. and Rutgers Physics. I hope that he sees it.

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    18th January 2018
    ATLAS Collaboration

    1
    Normalised differential cross-sections as a function of the mass of the two charged leptons and the b-jet unfolded from data, compared with selected Monte Carlo models. (Image: ATLAS Collaboration/CERN)

    The production of top quarks in association with vector bosons is a hot topic at the LHC. ATLAS first reported strong evidence for the production of a top quark in association with a Z boson at the EPS 2017 conference. In a paper submitted to the Journal of High-Energy Physics, the ATLAS experiment describes the measurement of top-quark production in association with a W boson in 13 TeV collisions.

    The new ATLAS result using the full 2015 and 2016 dataset extracts differential cross-sections for the production of a top quark in association with a W boson for the first time. This is particularly complex as top quarks almost always decay into a b quark and a W boson, and thus there are two W bosons in final state that decay very quickly. Events are selected that contain two charged leptons (electrons or muons), a jet that is identified as containing a hadron with a b quark, and missing transverse momentum due to the presence of neutrinos.

    Multivariate techniques are used to suppress large background contributions, especially from the production of a top quark with a top antiquark that occurs with much larger rate. They achieve a signal to background ratio of about 1:2, which allows the signal cross-section to be extracted as a function of kinematic observables. The measured background-subtracted distributions are corrected to remove the effects of experimental resolution so that they can be directly compared with theoretical predictions.

    Differential cross-sections as a function of several variables related to both the event and top quark or W boson kinematic properties have been measured and compared to theory predictions, implemented in different Monte Carlo programmes. The figure shows one out of the six extracted cross-sections.

    The uncertainty on the measurements is at the 20­-50% level, dominated by statistical effects. While this does not allow to draw firm conclusions, the data tend to have more events with high-momentum final-state objects than predicted. This effect can be seen in the figure. A quantitative analysis reveals, however, that the tested Monte Carlo models are all statistically compatible with the data. As ATLAS continues to study this channel, the increased size of the data sample and improvements in the predictions should make such comparisons more significant.

    Links:

    Measurement of differential cross-sections of a single top quark produced in association with a W boson at 13 TeV with ATLAS (arXiv: 1712.01602, see figures ).
    Measurement of the cross-section for producing a W boson in association with a single top quark in pp collisions at 13 TeV with ATLAS (arXiv: 1612.07231).
    Measurement of the production cross-section of a single top quark in association with a Z boson in proton-proton collisions at 13 TeV with the ATLAS detector (ATLAS-CONF-2017-052).
    See also the full lists of ATLAS Conference Notes and ATLAS Physics Papers.

    See the full article here .

    CERN LHC Map
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    LHC at CERN

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  • richardmitnick 2:52 pm on January 16, 2018 Permalink | Reply
    Tags: , , , HEP, , , , , 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.

    2
    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 4:36 pm on January 8, 2018 Permalink | Reply
    Tags: Accelerating science, , , Building collaborations, , , , HEP, MUSE and NEWS are two grant programs by which nearly 150 European scientists come to Fermilab to help advance its research, MUSE and NEWS are two new endeavors at the DOE Office of Science’s FNAL,   

    From FNAL: “MUSE and NEWS are on the RISE” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    January 8, 2018
    No writer credit found

    MUSE and NEWS are two new endeavors at the DOE Office of Science’s Fermilab, the U.S.’s premier particle physics laboratory. And contrary to what some physics fans might infer, the acronyms don’t stand for science experiments.

    They’re two new bridge-building grant programs that are designed to enable scientists from Europe to conduct particle physics research at Fermilab.

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    Muon g-2 is one of the Fermilab experiments that European scientists work on through the MUSE agreement. Photo: Reidar Hahn

    FNAL G-2 magnet from Brookhaven Lab finds a new home in the FNAL Muon G-2 experiment


    FNAL Muon g-2 studio

    RISE to the occasion

    MUSE and NEWS are two grant programs by which nearly 150 European scientists come to Fermilab to help advance its research, in particular on the laboratory’s muon experiments and superconducting accelerator technology. Their contributions total the equivalent of $15 million in salaried work.

    The European Commission H2020 research and innovation program provides funding for the NEWS and MUSE projects through the Marie Sklodowska-Curie Research and Innovation Staff Exchange (RISE) action. (The European Commission is the executive body of the European Union.)

    The RISE scheme promotes international and cross-sector collaboration through the exchange research and innovation staff and by sharing knowledge and ideas from research to market (and vice versa).

    “Everybody wins,” said Simone Donati of the University of Pisa, who is also a NEWS co-coordinator. “The European institutions benefit because they receive money to travel here. Fermilab benefits because it has placed several institutions into the networks. The people benefit. And the networks should last for a long time, even after the projects’ completion.”

    Building collaborations

    3
    MUSE exchange scientists also work on Mu2e. Photo: Reidar Hahn

    FNAL Mu2e solenoid


    FNAL Mu2e facility

    Accelerating science

    MUSE, which started in 2016, is coordinated by INFN researcher Simona Giovannella and supports roughly 70 scientists from universities and research institutes in Germany, Greece, Italy and the UK to work on Fermilab’s Mu2e and Muon g-2 experiments. The European scientists will contribute to an impressive 400 months’ worth of contributed work over four years to help further the cutting-edge particle detector technologies needed to look for hidden or rare particles predicted by theory but, as of now, never observed by experiment. Fermilab scientist Doug Glenzinski coordinates this activity at the lab.

    NEWS was proposed a year later, in 2016, to advance a number of fields in particle physics. Through NEWS, scientists from Germany, Greece, Italy and Sweden come to Fermilab to study muon physics and superconducting accelerator science. They also go to Caltech, NASA, SLAC National Accelerator Laboratory, and U.S. companies, as well as to the Japanese National Astronomical Observatory in Japan.

    Fermilab in particular will enjoy 100 months’ worth of contributed work over four years through NEWS, beginning in 2018. The roughly 60 visiting scientists will work on superconducting technologies for particle accelerators and detectors. Barzi coordinates this activity at Fermilab.

    (And in case you wondered: NEWS is short for “NEw WindowS on the universe and technological advancements from trilateral EU-US-Japan collaboration.” The MUSE acronym is more straightforward: “Muon campus in the U.S. and European contributions.” Acronymization is an art, not a science.)

    Reaching out through RISE

    3
    NEWS enables European scientists to work on superconducting accelerator and detector technologies at Fermilab. Photo: Reidar Hahn

    Outreach is a crucial component of participation in a RISE-funded program. MUSE and NEWS scientists at Fermilab are required to conduct science outreach in some way during their time at the lab. Many, for example, participate in the laboratory’s international summer students program, which was initially established by University of Pisa Professor Emeritus Giorgio Bellettini for visiting Italian university students in 1984.

    “The summer student program is just one example,” Donati said. “There are many other initiatives that we organize at Fermilab and other institutions, such as teaching seminars by experts in their field and physics nights at historical venues.”

    It’s all a part of the benefits-of-networks ethos in science, and for RISE in particular. The connections made in particle physics do more than advance research careers. They attract the next generation of scientists and benefit humanity.

    “RISE says, ‘We give you money to do your excellent research, and this research must not be confined within a library or laboratory,’” Donati said. “You have to show to the public that this is important, that it’s important for society, that people in science find good jobs so that the younger generations are encouraged to pursue a career in science.”

    MUSE and NEWS are just two manifestations of the principle, and Barzi expects to see a resulting expansion and strengthening of the research community.

    “We’re making practical use of a European funding agency for science, expanding our funding resources,” Barzi said. “Networks tend to increase because they keep branching out and branching out. They naturally expand because you involve people who are interested in that area of science, and they kind of naturally come to you.”

    She adds, “You can use your skills and knowledge to contribute outside your own narrow, specialized field. This is what I find most exciting.”

    Further details about RISE work plan 2018-2020 and the upcoming call for proposals is available online.

    See the full article here .

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    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 3:56 pm on January 8, 2018 Permalink | Reply
    Tags: , , , HEP, Lithuania becomes Associate Member State of CERN, , ,   

    From CERN: “Lithuania becomes Associate Member State of CERN” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    8 Jan 2018
    Harriet Kim Jarlett

    1
    CERN Director General, the Minister of Foreign Affairs of the Republic of Lithuania and the President of the Republic of Lithuania at the signing of the agreement (Image: Robertas Dačkus/Office of the President of the Republic of Lithuania).

    Today, the Republic of Lithuania became an Associate Member State of CERN. This follows official notification to CERN that the Republic of Lithuania has completed its internal approval procedures, as required for the entry into force of the Agreement, signed in June 2017, granting that status to the country.

    Lithuania’s relationship with CERN dates back to 2004, when an International Cooperation Agreement was signed between the Organization and the government of the Republic of Lithuania setting priorities for the further development of scientific and technical cooperation between CERN and Lithuania in high-energy physics. One year later, in 2005, a Protocol to this Agreement was signed, paving the way for the participation of Lithuanian universities and scientific institutions in high-energy particle physics experiments at CERN.

    Lithuania has contributed to the CMS experiment since 2007 when a Memorandum of Understanding (MoU) was signed marking the beginning of Lithuanian scientists’ involvement in the CMS collaboration. Lithuania has also played an important role in database development at CERN for CMS data mining and data quality analysis. Lithuania actively promoted the BalticGrid in 2005.

    In addition to its involvement in the CMS experiment, Lithuania is part of two collaborations that aim to develop detector technologies to address the challenging upgrades needed for the High-Luminosity LHC.

    Since 2004, CERN and Lithuania have also successfully collaborated on many educational activities aimed at strengthening the Lithuanian particle physics community. Lithuania has been participating in the CERN Summer Student programme and 53 Lithuanian teachers have taken part in CERN’s high-school teachers programme.

    The associate membership of Lithuania strengthens the long-term partnership between CERN and the Lithuanian scientific community. Associate Membership allows Lithuania to take part in meetings of the CERN Council and its committees (Finance Committee and Scientific Policy Committee). It also makes Lithuanian scientists eligible for staff appointments. Finally, Lithuanian industry is henceforth entitled to bid for CERN contracts, thus opening up opportunities for industrial collaboration in areas of advanced technology.

    See the full article here.

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  • richardmitnick 11:31 am on December 20, 2017 Permalink | Reply
    Tags: , , , CMS releases more than one petabyte of open data, HEP, , ,   

    From CERN: “CMS releases more than one petabyte of open data” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    20 Dec 2017
    Corinne Pralavorio

    1
    A collision event recorded by CMS in 2012 showing a “Higgs candidate”, available on the CERN Open Data portal with the latest release of CMS Open Data. (Image: Tom McCauley/CMS/CERN)

    The CMS Collaboration at CERN have just made public around half of the data collected in 2012 by the CMS detector at the Large Hadron Collider. This release includes sets used to discover the Higgs boson, and is being shared through the CERN Open Data portal.

    This is the third release of high-level CMS Open Data, following the release of 2010 data in 2014, and 2012 data in 2016. This batch contains more than 550 terabytes of proton-proton collision data recorded at a centre-of-mass energy of 8 TeV as well as around 510 petabytes of Monte Carlo simulation data.

    LHC data are complicated and big. CMS researchers have recorded petabytes of data from collisions at the LHC and have so far published hundreds of scientific papers with them. By releasing the data into the public domain, researchers outside the CMS Collaboration have the opportunity to conduct novel research with them.

    “Our data are an important element of the CMS Collaboration’s rich scientific legacy,” says CMS Spokesperson, Joel Butler. “We would like to ensure that they are not only preserved in the long run but are also available to the public, so that both CMS members and external researchers can re-examine them in the future. This is part of our commitment to openness and long-term data preservation.”

    2
    Animation showing a “Higgs candidate” event, recorded by CMS in 2012 and available on the CERN Open Data portal with the latest release of CMS Open Data. (Image: Tom McCauley and Achintya Rao CMS/CERN)

    Recently, the first two such research papers were published by a team of theorists at MIT interested in performing a measurement CMS scientists had themselves not done: specifically they wanted to measure particular substructures in clusters of particles known as “jets” produced in proton-proton collisions.

    The latest release of CMS Open Data also carries the fascinating possibility of allowing people to repeat the analysis that led to the Higgs discovery by studying the same data used by CMS scientists to announce the particle’s existence in 2012. As a proof of concept, CMS doctoral student Nur Zulaiha Jomhari analysed CMS Open Data and produced plots similar to some of those shown when the Higgs discovery was announced. This analysis is a lot less sophisticated than the official CMS one and is not scrutinised by the wider CMS community of experts, but it demonstrates the potential of CMS Open Data.

    2
    Left: The official CMS plot for the “Higgs to four leptons” channel, shown on the day of the Higgs discovery announcement. Right: A similar plot produced by Nur Zulaiha Jomhari et al. using CMS Open Data from 2011 and 2012. Although the plots appear similar, the analysis with CMS Open Data uses more data (at 8 TeV and overall) than the official CMS one from the original discovery but is a lot less sophisticated and is not scrutinised by the wider CMS community of experts. (Image: CMS/CERN)

    In addition to the datasets themselves, the CMS Data Preservation and Open Data team has also assembled a comprehensive collection of supplementary materials, including example code for performing relatively simple analyses, as well as metadata such as information on how data were selected and what the LHC’s running conditions were during the time of data collection.

    At the moment, CMS has committed to releasing up to 50% of each year’s recorded data a few years after they were collected, once CMS scientists finish most of their analysis of these datasets. “To see our open data in use outside CMS has been very rewarding,” says Kati Lassila-Perini, the CMS Data Preservation and Open Access co-coordinator. “It has been a great motivation for us and we look forward to continuing our pioneering efforts to release research-quality open data from the LHC in the years to come.”

    Read more about this release in the CMS announcement

    See the full article here.

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  • richardmitnick 4:30 pm on December 19, 2017 Permalink | Reply
    Tags: , , CERN Large Hadron Collider, , , HEP, , Large Electron-Positron Collider, , , , , ,   

    From Symmetry: “Machine evolution” 

    Symmetry Mag
    Symmetry

    12/19/17
    Amanda Solliday

    1
    Courtesy of SLAC

    Planning the next big science machine requires consideration of both the current landscape and the distant future.

    Around the world, there’s an ecosystem of large particle accelerators where physicists gather to study the most intricate details of matter.

    These accelerators are engineering marvels. From planning to construction to operation to retirement, their lifespans stretch across decades.

    But to get the most out of their investments of talent and funding, laboratories planning such huge projects have to think even longer-term: What could these projects become in their next lives?

    The following examples show how some of the world’s big physics machines have evolved to stay at the forefront of science and technology.

    Same tunnel, new collisions

    Before CERN research center in Geneva, Switzerland, had its Large Hadron Collider, it had the Large Electron-Positron Collider. LEP was the largest electron-positron collider ever built, occupying a nearly 17-mile circular tunnel dug beneath the border of Switzerland and France. The tunnel took three years to completely excavate and build.

    The first particle beam traveled around the LEP circular collider in 1989. Long before then, the international group of CERN physicists and engineers were already thinking about what CERN’s next machine could be.

    “People were saying, ‘Well, if we do build LEP, then we should make it compatible with the [then-proposed] Large Hadron Collider,’” says James Gillies, a senior communications advisor and member of the strategic planning and evaluation unit at CERN. “If you want to have a future facility, you often have to engage the people who just finished designing one machine to start thinking about the next one.”

    LEP’s designers chose an energy for the collider that would mass-produce Z bosons, fundamental particles discovered by earlier experiments at CERN. The LHC would be a step up from LEP, reaching higher energies that scientists hoped could produce the Higgs boson. In the 1960s, theorists proposed the Higgs as a way to explain the origin of the mass of elementary particles. And the new machine to look for it could be built in the same 17-mile tunnel excavated for LEP.

    Engineers began working on the LHC while LEP was still running. The new machine required enlargements to underground areas—it needed bigger detectors and new experimental halls.

    “That was challenging because these caverns are huge. As they were being excavated, the pressure on the LEP tunnel was reduced and the LEP beamline needed realignment,” Gillies says. “So you constantly had to realign the collider for experiments as you were digging.”

    After LEP reached its highest energy in 2000, it was switched off. The tunnel remained the same, says Gillies, but there were many other changes. Only one of the LEP detectors, DELPHI, remains underground at CERN as a visitors’ point.

    In 2012, LHC scientists announced the discovery of the long-sought Higgs boson. The LHC is planned to continue running until at least 2035, gradually increasing the intensity of its particle collisions. The research and development into the accelerator’s successor is already happening. The possibilities include a higher energy LHC, a compact linear collider or an even larger circular collider.

    2

    Large Electron-Positron Collider
    Location: CERN—Geneva, Switzerland
    First beam: 1989
    Link to LEP Timeline: Timeline
    Courtesy of CERN

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Large Hadron Collider
    Location: CERN—Geneva, Switzerland
    First beam: 2008
    Link to LHC Timeline: Timeline
    Courtesy of CERN

    High-powered science
    Decades before the LHC came into existence, a suburb of Chicago was home to the most powerful collider in the world: the Tevatron. A series of accelerators at Fermi National Accelerator Laboratory boosted protons and antiprotons to nearly the speed of light. In the final, 4-mile Tevatron ring, the particles reached record energy levels, and more than 1000 superconducting magnets steered them into collisions. Physicists used the Tevatron to make the first direct measurement of the tau neutrino and to discover the top quark, the last observed lepton and quark, respectively, in the Standard Model.

    The Tevatron shut down in 2011 after the LHC came up to speed, but the rest of Fermilab’s accelerator infrastructure was still hard at work powering research in particle physics—particularly on the abundant, mysterious and difficult-to-detect neutrino.

    Starting in 1999, a brand-new, 2-mile circular accelerator called the Main Injector was added to the Fermilab complex to increase the number of Tevatron particle collisions tenfold. It was joined in its tunnel by the Recycler, a permanent magnet ring that stored and cooled antiprotons.

    But before the Main Injector was even completed, scientists had identified a second purpose: producing powerful beams of neutrinos for experiments in Illinois and 500 miles away in Minnesota.

    FNAL/NOvA experiment map

    By 2005, the proton beam circulating in the Main Injector was doing double duty: sending ever-more-intense beams to the Tevatron collider and smashing into a target to produce neutrinos. Following the shutdown of the Tevatron, the Recycler itself was recycled to increase the proton beam power for neutrino research.

    “I’m still amazed at how we are able to use the Recycler. It can be difficult to transition if a machine wasn’t originally built for that purpose,” says Ioanis Kourbanis, the head of the Main Injector department at Fermilab.

    Fermilab’s high-energy neutrino beam is already the most intense in the world, but the laboratory plans to enhance it with future improvements to the Main Injector and the Recycler, and to build a brand-new neutrino beamline.

    Neutrinos almost never interact with matter, so they can pass straight through the Earth on their way to detectors onsite and others several hundred miles away. Scientists hope to learn more about neutrinos and their possible role in shaping our early universe.

    The new beamline will be part of the Long-Baseline Neutrino Facility, which will send neutrinos 800 miles underground to the massive, mile-deep detectors of the Deep Underground Neutrino Experiment.

    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

    Scientists from around the world will use the DUNE data to answer questions about neutrinos, thanks to the repurposed pieces of the Fermilab accelerator complex.

    5

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    Tevatron
    Location: Fermilab—Batavia, Illinois
    First beam: 1983
    Link to Tevatron Timeline: Timeline
    Courtesy of Fermilab

    6

    Neutrinos at the Main Injector (NuMI) beam
    Location: Fermilab—Batavia, Illinois
    First beam: 2004
    Link to Fermilab Timeline: Timeline
    Courtesy of Fermilab

    A monster accelerator

    When physicists first came up with the idea to build a two-mile linear accelerator at what is now called SLAC National Accelerator Laboratory, managed by Stanford University, they called it “Project M” for “Monster.” Engineers began building it from hand-drawn designs. Once completed, the machine was able to accelerate electrons to near the speed of light, producing its first particle beam in May 1966.

    SLAC Campus

    The accelerator’s scientific purpose has gone through several iterations of particle physics experiments over the decades, from fixed-target experiments to the Stanford Linear Collider (the only electron-positron linear collider ever built) to an injector for a circular collider, the Positron-Electron Project.

    These experiments led to the discovery that protons are made of quarks, the first evidence that the charm quark existed (through observations of the J/psi particle, co-discovered with researchers at MIT) and the discovery of the tau lepton.

    In 2009, the lab used the accelerator as the backbone for a different type of science machine—an X-ray free-electron laser, the Linac Coherent Light Source.

    “Looking around, SLAC was the only place in the world with a linear accelerator capable of driving a free-electron laser,” says Claudio Pellegrini, a distinguished professor emeritus of physics at the University of California, Los Angeles and a visiting scientist and consulting professor at SLAC. Pellegrini first proposed the idea to transform SLAC’s linear accelerator.

    The new machine, a DOE Office of Science user facility, would be the world’s first laser of its kind that could produce extremely bright hard X-rays, the high-energy X-rays that let scientists take snapshots of atoms and molecules.

    “Much of the physics and many of the tools learned and developed during the operation of the Stanford Linear Collider were directly applicable to the free electron laser,” says Lia Merminga, head of the accelerator directorate at SLAC. “This was a big factor in the LCLS being commissioned in record time. Without the Stanford Linear Collider experience, this significant body of work would have to be reinvented and reproduced almost from scratch.”

    Little about the accelerator itself needed to change. But to create a free-electron laser, scientists needed to design a new part: an electron gun, a device that generates electrons to be injected into the accelerator. A collaboration of several national labs and UCLA created a new type of electron gun for LCLS, while other national labs helped build undulators, a series of magnets that would wiggle the electrons to create X-rays.

    LCLS used only the last third of SLAC’s original linear accelerator. In part of the remaining section, scientists are developing plasma wakefield and other new particle acceleration techniques.

    For the X-ray laser’s next iteration, LCLS-II, scientists are aiming for an even brighter laser that will fire 1 million pulses per second, allowing them to observe rare and exceptionally transient events.

    SLAC/LCLS II

    To do this, they will need to replace the original copper structures with superconducting technology. The technology is derived from designs for a large International Linear Collider [ILC] proposed to be built in Japan.

    ILC schematic

    “I’m in awe of the foresight of the original builders of SLAC’s linear accelerator,” Merminga adds. “We’ve been able to do so much with this machine, and the end is not yet in sight.”

    7

    Fixed target and collider experiments

    Location: SLAC—Menlo Park, California
    First beam: 1966
    Link to SLAC Timeline: Timeline
    Courtesy of SLAC

    8

    Linac Coherent Light Source
    Location: SLAC—Menlo Park, California
    First beam: 2009
    Link to SLAC Timeline: Timeline
    Courtesy of SLAC

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 5:41 pm on December 18, 2017 Permalink | Reply
    Tags: , , , HEP, Higgsinos?, , ,   

    From CERN ATLAS: “Searching for supersymmetric Higgs bosons on the compressed frontier” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    18th December 2017
    ATLAS Collaboration

    1
    Figure 1: The distribution of the di-electron or di-muon invariant mass (mll), where the signal events tend to cluster at low values of mll. Solid histograms indicate Standard Model background processes, points with error bars indicate the data, and the dashed lines indicate hypothetical Higgsino events. The bottom plot shows the ratio of the data to the total Standard Model background. (Image: ATLAS Collaboration/CERN)

    The Standard Model has a number of puzzling features. For instance, why does the Higgs boson have a relatively low mass? Could its mass arise from a hidden symmetry that keeps it from being extremely heavy? And what about dark matter? While the Standard Model has some (almost) invisible particles, like neutrinos, those particles can’t account for all of the dark matter observed by cosmological measurements.

    These puzzles could be solved by supersymmetry, a theory that provides a natural mechanism for protecting the Higgs mass and also has a dark matter candidate.

    Standard model of Supersymmetry DESY

    Supersymmetry predicts the existence of “super-partner” particles that are heavier than their Standard Model counterparts. As long as the supersymmetric partners of the Higgs boson, called “higgsinos”, aren’t too heavy, then supersymmetry can explain a Higgs mass consistent with current observations. The lightest higgsino, the “LSP” (for “lightest supersymmetric particle”), would be a dark matter candidate, while heavier higgsinos decay to the LSP along with other particles like electrons or muons.

    Detecting higgsinos can be difficult, especially if the heavier higgsinos and the LSP have very similar masses. In such “compressed” scenarios, the electrons and muons from the heavier higgsino decays have very low momenta, making them difficult to detect. In recent years, ATLAS has made significant progress in understanding these low-momentum particles, which has opened the door to new searches.

    2
    Figure 2: Limits on Higgsino production from the soft-lepton analysis described here (in blue) and a separate search for “disappearing” tracks. The mass of the heavier charged Higgsino is on the horizontal axis, while the difference in mass between the heavier Higgsino and the LSP is shown on the vertical axis. The dashed lines and solid fill show the expected limits (assuming no signal) and observed limits, respectively, where models within the filled areas are excluded. The grey region represents the models excluded by the LEP experiments. (Image: ATLAS Collaboration/CERN)

    In December 2017, ATLAS presented new updates in the compressed supersymmetry search at the SUSY17 conference. These latest results exploit unique features of higgsino decays, most importantly how the small mass difference between the higgsinos causes the electron or muon pair to have a correspondingly small mass, as illustrated in Figure 1. The data are consistent with the Standard Model predictions and have thus been used to set limits on higgsino masses. The new limits are shown in Figure 2, along with limits from another recent ATLAS search that probes SUSY models with even more compressed spectra. For the first time, these LHC results surpass constraints set in 2004 by the Large Electron Positron (LEP) collider that was hosted in the same 27 km circumference tunnel that now holds the LHC.

    As many of the still viable supersymmetry scenarios have very small higgsino mass differences, there remains plenty of room for investigation. Look forward to new searches of the compressed frontier as ATLAS continues to collect and analyse data from the LHC.

    Links:
    See the full article for further references with links.

    See the full article here .

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

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    CERN Courier

    QuantumDiaries


    Quantum Diaries

     
  • richardmitnick 3:21 pm on December 13, 2017 Permalink | Reply
    Tags: , , , HEP, , ,   

    From FNAL: “Photons continue to enlighten physicists” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    December 13, 2017
    Andy Beretvas
    Alessandra Lucà

    You may be familiar with particles of light, called photons. Physicists give the name “prompt photons” to those that are produced by two particles smashing together — hard collisions — as contrasted with those resulting from the decay of other particles. The Tevatron produced prompt photons by the hard collisions between protons and antiprotons.

    Knowing the likelihood that proton-antiproton collisions will produce prompt photons tells us something about the proton’s components, which are called quarks and gluons. In particular, we can learn about the density of quarks and gluons inside the colliding protons and get a better grasp on how they fragment into photons. These ingredients are all described in a theory called perturbative quantum chromodynamics.

    1
    The cross section is presented as a function of the transverse energy of the photon.

    2
    This plot compares three models — Pythia 6.216, Sherpa 1.4.1 and MCFM 6.8 — to the data.

    Prompt photons at hadron colliders constitute an important test of perturbative quantum chromodynamics (pQCD), and may also be found in signatures of new physics processes. A precise measurement of prompt photon production is important to probe theoretical models, as well as to gain a better understanding of final states that contain energetic photons.

    CDF physicists used the full Tevatron Run II data set, which contained 2.1 million collision events in the selected sample, to measure the prompt photons’ energies.

    FNAL/Tevatron CDF detector

    The researchers were particularly interested in the energy they carried in a direction perpendicular to the colliding beams, a property called transverse energy.

    The photons’ transverse energy tells you something about the process that produced it. Photons with less than 100 GeV of transverse energy were generated primarily by quarks and gluons scattering off each other. At higher energies, the dominant process was the annihilation of a quark with its antimatter counterpart.

    CDF conducted a similar study to this one in 2009. An important part of the measurement is that the photons should be isolated (the energy deposited near the photon is small). This time, a larger data set meant scientists could study a larger range of transverse photon energy, from 30 to 500 GeV. Moreover, a different statistical technique has been developed to better identify prompt photons; their identification is very challenging because of the huge background coming from other particles (mostly hadrons).

    The results are presented in the first figure: The likelihood of proton-antiproton collisions producing a prompt photon decreases with increasing transverse energy. Note the data covers six orders of magnitude. This provides a challenge for theorists to come up with models that predicts this behavior correctly over so large a range.

    Over the full range, data shows good agreement with the MCFM prediction. This model is a next-to-leading order pQCD calculation developed by Fermilab physicists John Campbell, Keith Ellis, Walter Giele and Ciaran Williams.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 10:47 am on December 6, 2017 Permalink | Reply
    Tags: , , FAST Fermilab Accelerator Science and Technology, FNAL IOTA ring, HEP, , ,   

    From FNAL: “FAST electron beam achieves milestone energy for future accelerator R&D” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    December 6, 2017
    Tom Barratt

    1
    The linear accelerator at the Fermilab Accelerator Science and Technology facility recently ramped up a beam of electrons to 300 MeV, surpassing the threshold needed to launch a new accelerator physics program at Fermilab. Photo: Giulio Stancari.

    On Nov. 15, a team at the Fermilab Accelerator Science and Technology (FAST) facility ramped up a beam of electrons to 300 million electronvolts.

    It was a double milestone event. For one, the beam surpassed the threshold needed to launch a new accelerator physics program at Fermilab supported by the DOE Office of Science. The driving goal of the FAST facility is to support a new R&D accelerator that will require a minimum of 150 million electronvolts (MeV) of electron beam energy.

    “It’s a great achievement and an important milestone for the project and the laboratory,” said Jerry Leibfritz, project engineer for FAST.

    It was also a hard-earned success for the larger particle accelerator community. For the first time anywhere, the Fermilab group achieved a beam energy of 250 MeV from a single ILC-type cryomodule. For years, a worldwide R&D effort has been under way to develop cryomodules — accelerating structures — for the proposed International Linear Collider under development by a broad international collaboration for possible construction in Japan. The beam energy milestone was one of the goals of the international ILC R&D effort.

    ILC schematic

    “Fermilab has been known for its outstanding proton beams,” said Vladimir Shiltsev, head of the Fermilab Accelerator Physics Center. “Getting to a 300 MeV electron beam is a big deal for Fermilab’s accelerator R&D. We’re happy we could advance this R&D on two fronts.”

    The delivery of the high-energy electron beam enables the start of the accelerator research program at FAST and demonstrates that the facility is up to the job of supporting the future Integrable Optics Test Accelerator, or IOTA, scheduled to come online in mid-2018.

    The IOTA idea

    2
    FNAL IOTA ring schematic.

    The team behind IOTA, a 40-meter-circumference ring, is looking to break new ground in beam physics research. Once it is operable, scientists and engineers will inject beams of electrons from FAST accelerators into the ring, where they can be maintained and used to carry out R&D for new, advanced accelerator equipment and techniques.

    Although technology behind accelerator-based particle physics has made huge strides over recent decades, all current accelerators use magnets with linear focusing to stabilize and guide particle beams. The technique can only advance so far, however, before fundamental physics effects, which tend to destabilize beams, limit the experimental possibilities.

    To solve this problem, Fermilab began a research program to develop a number of novel accelerator techniques, and IOTA will be the pinnacle of this effort. Scientists from around the world will be able to use the next-generation accelerator to collaborate and test innovative ideas, finding ways around the physics constraints to reach the next level of accelerator beam power.

    For IOTA to carry out successful research, the FAST scientists chose a minimum threshold of energy for the injected particles.

    “Generally speaking, the more energy, the better the particle stability, but then you have to increase the technical complexity,” said Alexander Valishev, Fermilab scientist and head of the IOTA/FAST Department. “We chose 150 MeV as the electron energy for IOTA because it’s a good balance between energy and expense.”

    The team used a specialized beamline to produce the high-energy electron beam.

    “One of the biggest challenges in achieving this milestone was just getting all the complex systems and components of the accelerator to integrate and work together,” Valishev said.

    3
    The Fermilab Accelerator Science and Technology facility supports the research and development of accelerator technology for the next generation of particle accelerators. Photo: Jerry Leibfritz

    World-record beam

    In one sense, it was an achievement decades in the making. At the core of the electron-beam accelerator are superconducting elements whose development at Fermilab began in earnest in the late 1990s. That was the start of the development of SRF — superconducting radio-frequency technology — at Fermilab.

    SRF is the technology of choice for many current and future particle accelerators, including machines under construction now in the United States and Germany, Fermilab’s PIP-II accelerator that will provide high-intensity beams for neutrino experiments, and the proposed ILC. The ILC’s technical design, completed in 2012, requires that each 12-meter-long unit of the accelerator, called a cryomodule, deliver an electron beam energy gain of 250 MeV at a particular maxiumum gradient, which is a measure of how much energy the beam gains over a given distance. It was a formidable task for SRF experts and accelerator physicists worldwide.

    Now the highest-energy beam ever accelerated through the ILC-type cryomodule at design specifications has been demonstrated at Fermilab.

    “In October 2014 Fermilab successfully operated the superconducting elements in this cryomodule to the nominal ILC gradient, but without accelerating an actual electron beam. The milestone achieved this month proves the expected performance definitively,” said physicist Marc Ross of SLAC National Accelerator Laboratory. “The work done over the last years has paid off, the calibrations were correct, and the cryomodule delivered as required. It is a critical milestone toward the realization of ILC.”

    FAST friends

    The FAST team are now engaged in joint experiments with external collaborators, such as physicists from Northern Illinois University, the University of Chicago and Los Alamos National Laboratory.

    “We are very happy to have another working accelerator at Fermilab,” Valishev said. “FAST and IOTA will enable high-impact research and will be very useful for establishing more international collaboration.”

    The IOTA/FAST collaboration currently has 27 partners, including CERN and the University of Oxford. The team aims to finish the ring’s construction by early 2018 and to have it up and running by the summer. Injections of protons into the IOTA ring is expected a year later.

    “This is a tremendous accomplishment for all of us who have been involved in building this facility for the past decade,” Leibfritz said. “In 2006, a small group of us laid the first concrete blocks for the FAST test cave. This successful acceleration of beam really is the greatest testament to everyone who’s been involved in making it a reality.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    FNAL Icon
    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
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