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  • richardmitnick 10:07 pm on May 13, 2021 Permalink | Reply
    Tags: "Why precision luminosity measurements matter", , , , CERN CMS, , , , , ,   

    From European Organization for Nuclear Research (Organisation européenne pour la recherche nucléaire)(EU) [CERN]: “Why precision luminosity measurements matter” 

    Cern New Bloc

    Cern New Particle Event

    From European Organization for Nuclear Research (Organisation européenne pour la recherche nucléaire)(EU) [CERN]

    12 May, 2021
    Piotr Traczyk

    Both the CMS and ATLAS experiments have performed luminosity measurements with spectacular precision.

    1
    The interaction region of the CMS experiment right before the installation of the new beam pipe. (Image: CERN)

    The ATLAS and CMS experiments at the Large Hadron Collider (LHC) have performed luminosity measurements with spectacular precision. A recent physics briefing from CMS complements earlier ATLAS results and shows that by combining multiple methods, both experiments have reached a precision better than 2%. For physics analyses – such as searches for new particles, rare processes or measurements of the properties of known particles – it is not only important for accelerators to increase luminosity, but also for physicists to understand it with the best possible precision.

    Luminosity is one of the fundamental parameters to measure an accelerator’s performance. In the LHC, the circulating beams of protons are not continuous beams but are grouped into packets, or “bunches”, of about 100 billion protons. These bunches collide with oncoming bunches 40 million times per second at the interaction points within particle detectors. But when two such bunches pass through each other, only a few protons from each bunch end up interacting with the protons circulating in the opposite direction. Luminosity is a measure of the number of these interactions. Two main aspects of luminosity are instantaneous luminosity, describing the number of collisions happening in a unit of time (for example every second), and integrated luminosity, measuring the total number of collisions produced over a period of time.

    Integrated luminosity is usually expressed in units of “inverse femtobarns” (fb-1). A femtobarn is a unit of cross-section, a measure of the probability for a process to occur in a particle interaction. This is best illustrated with an example: the total cross-section for Higgs boson production in proton–proton collisions at 13 TeV at the LHC is of the order of 6000 fb. This means that every time the LHC delivers 1 fb-1 of integrated luminosity, about 6000 fb x 1 fb-1 = 6000 Higgs bosons are produced.

    Knowing the integrated luminosity allows physicists to compare observations with theoretical predictions and simulations. For example, physicists can look for dark matter particles that escape collisions undetected by looking at energies and momenta of all particles produced in a collision. If there is an imbalance, it could be caused by an undetected, potentially dark matter, particle carrying energy away. This is a powerful method of searching for a large class of new phenomena, but it has to take into account many effects, such as neutrinos produced in the collisions. Neutrinos also escape undetected and leave an energy imbalance, so in principle, they are indistinguishable from the new phenomena. To see if something unexpected has been produced, physicists have to look at the numbers.

    So if 11000 events show an energy imbalance, and the simulations predict 10000 events containing neutrinos, this could be significant. But if physicists only know luminosity with a precision of 10%, they could have easily had 11000 neutrino events, but there were just 10% more collisions than assumed. Clearly, a precise determination of luminosity is critical.

    There are also types of analyses that depend much less on absolute knowledge of the number of collisions. For example, in measurements of ratios of different particle decays, such as the recent LHCb measurement.

    Here, uncertainties in luminosity get cancelled out in the ratio calculations. Other searches for new particles look for peaks in mass distribution and so rely more on the shape of the observed distribution and less on the absolute number of events. But these also need to know the luminosity for any kind of interpretation of the results.

    Ultimately, the greater the precision of the luminosity measurement, the more physicists can understand their observations and delve into hidden corners beyond our current knowledge.

    See the full article here.


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    Meet CERN in a variety of places:

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    Cern Courier


    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    ALICE

    CMS

    LHCb

    LHC

    OTHER PROJECTS AT CERN

    European Organization for Nuclear Research (Organisation européenne pour la recherche nucléaire)(EU)[CERN] AEGIS.


    CERN FASER is designed to study the interactions of high-energy neutrinos and search for new as-yet-undiscovered light and weakly interacting particles. Such particles are dominantly produced along the beam collision axis and may be long-lived particles, travelling hundreds of metres before decaying. The existence of such new particles is predicted by many models beyond the Standard Model that attempt to solve some of the biggest puzzles in physics, such as the nature of dark matter and the origin of neutrino masses.

     
  • richardmitnick 7:53 am on August 28, 2020 Permalink | Reply
    Tags: "CMS experiment at CERN releases fifth batch of open data", , , CERN CMS, , , , ,   

    From CERN CMS: “CMS experiment at CERN releases fifth batch of open data” 

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    From CERN CMS

    27 August, 2020
    Achintya Rao

    All research-quality data recorded by CMS during the first two years of LHC operation are now publicly available.

    1
    An artistic representation of the CMS detector made of pulsating lines. (Image: Achintya Rao/CERN.)

    The CMS collaboration at CERN has released into the open 18 new datasets, comprising proton–proton collision data recorded by CMS at the Large Hadron Collider (LHC) during the second half of 2011. LHC data are unique and are of interest to the scientific community as well as to those in education. Preserving the data and the knowledge to analyse them is critical. CMS has therefore committed to releasing its research data openly, with up to 100% being made available 10 years after recording them; the embargo gives the scientists working on CMS adequate time to analyse the data themselves.

    The total data volume of this latest release is 96 terabytes. Not only does this batch complement the data from the first half of 2011, released back in 2016, it also provides additional tools, workflows and examples as well as improved documentation for analysing the data using cloud technologies. The data and related materials are available on the CERN Open Data portal, an open repository built using CERN’s home-grown and open source software, Invenio.

    Previous releases from CMS included the full recorded data volume from 2010 and half the volumes from 2011 and 2012 (the first “run” of the LHC). Special “derived datasets”, some for education and others for data science, have allowed people around the world to “rediscover” the Higgs boson in CMS open data. Novel papers have also been published using CMS data, by scientists unaffiliated with the collaboration.

    In the past, those interested in analysing CMS open data needed to install the CMS software onto virtual machines to re-create the appropriate analysis environment. This made it challenging to scale up a full analysis for research use, a task that requires considerable computing resources. With this batch, CMS has updated the documentation for using software containers with all the software pre-installed and added workflows running on them, allowing the data to be easily analysed in the cloud, either at universities or using commercial providers. Some of the new workflows are also integrated with REANA, the CERN platform for reusable analyses.

    CMS and the CERN Open Data team have been working closely with current and potential users of the open data – in schools, in higher education and in research – to improve the services offered. The search functionality of the portal has been updated with feedback from teachers who participated in dedicated workshops at CERN in previous years, the documentation has been enhanced based on conversations with research users and a new online forum has been established to provide support. In September, CMS is organising a virtual workshop for theoretical physicists interested in using the open data.

    “We are thrilled to be able to release these new data and tools from CMS into the public domain,” says Kati Lassila-Perini, who has co-led the CMS project for open data and data preservation since its inception. “We look forward to seeing how the steps we have taken to improve the usability of our public data are received by the community of users, be it in education or in research.”

    You can read more about the latest open-data release from CMS on the CERN Open Data portal: opendata.cern.ch/docs/cms-completes-2010-2011-pp-data

    See the full article here.


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  • richardmitnick 3:27 pm on August 3, 2020 Permalink | Reply
    Tags: "CERN experiments announce first indications of a rare Higgs boson process", , , CERN CMS, , , , , , The ATLAS and CMS experiments at CERN have announced new results which show that the Higgs boson decays into two muons.   

    From CERN: “CERN experiments announce first indications of a rare Higgs boson process” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    3 August, 2020

    The ATLAS [below] and CMS [below] experiments at CERN have announced new results which show that the Higgs boson decays into two muons.

    1
    Candidate event displays of a Higgs boson decaying into two muons as recorded by CMS (left) and ATLAS (right). (Image: CERN)

    Geneva. At the 40th ICHEP conference, the ATLAS and CMS experiments announced new results which show that the Higgs boson decays into two muons. The muon is a heavier copy of the electron, one of the elementary particles that constitute the matter content of the Universe. While electrons are classified as a first-generation particle, muons belong to the second generation. The physics process of the Higgs boson decaying into muons is a rare phenomenon as only about one Higgs boson in 5000 decays into muons. These new results have pivotal importance for fundamental physics because they indicate for the first time that the Higgs boson interacts with second-generation elementary particles.

    Physicists at CERN have been studying the Higgs boson since its discovery in 2012 in order to probe the properties of this very special particle. The Higgs boson, produced from proton collisions at the Large Hadron Collider, disintegrates – referred to as decay – almost instantaneously into other particles. One of the main methods of studying the Higgs boson’s properties is by analysing how it decays into the various fundamental particles and the rate of disintegration.

    CMS achieved evidence of this decay with 3σ, which means that the chance of seeing the Higgs boson decaying into a muon pair from statistical fluctuation is less than one in 700. ATLAS’s 2σ result means the chances are one in 40 [strange, lower statistical signifance but greater probability, never saw that before] . The combination of both results would increase the significance well above 3σ and provides strong evidence for the Higgs boson decay to two muons.

    “CMS is proud to have achieved this sensitivity to the decay of Higgs bosons to muons, and to show the first experimental evidence for this process. The Higgs boson seems to interact also with second-generation particles in agreement with the prediction of the Standard Model, a result that will be further refined with the data we expect to collect in the next run,” said Roberto Carlin, spokesperson for the CMS experiment.

    The Higgs boson is the quantum manifestation of the Higgs field, which gives mass to elementary particles it interacts with, via the Brout-Englert-Higgs mechanism. By measuring the rate at which the Higgs boson decays into different particles, physicists can infer the strength of their interaction with the Higgs field: the higher the rate of decay into a given particle, the stronger its interaction with the field. So far, the ATLAS and CMS experiments have observed the Higgs boson decays into different types of bosons such as W and Z, and heavier fermions such as tau leptons. The interaction with the heaviest quarks, the top and bottom, was measured in 2018. Muons are much lighter in comparison and their interaction with the Higgs field is weaker. Interactions between the Higgs boson and muons had, therefore, not previously been seen at the LHC.

    Standard Model of Particle Physics, Quantum Diaries

    “This evidence of Higgs boson decays to second-generation matter particles complements a highly successful Run 2 Higgs physics programme. The measurements of the Higgs boson’s properties have reached a new stage in precision and rare decay modes can be addressed. These achievements rely on the large LHC dataset, the outstanding efficiency and performance of the ATLAS detector and the use of novel analysis techniques,” said Karl Jakobs, ATLAS spokesperson.

    What makes these studies even more challenging is that, at the LHC, for every predicted Higgs boson decaying to two muons, there are thousands of muon pairs produced through other processes that mimic the expected experimental signature. The characteristic signature of the Higgs boson’s decay to muons is a small excess of events that cluster near a muon-pair mass of 125 GeV, which is the mass of the Higgs boson. Isolating the Higgs boson to muon-pair interactions is no easy feat. To do so, both experiments measure the energy, momentum and angles of muon candidates from the Higgs boson’s decay. In addition, the sensitivity of the analyses was improved through methods such as sophisticated background modelling strategies and other advanced techniques such as machine-learning algorithms. CMS combined four separate analyses, each optimised to categorise physics events with possible signals of a specific Higgs boson production mode. ATLAS divided their events into 20 categories that targeted specific Higgs boson production modes.

    The results, which are so far consistent with the Standard Model predictions, used the full data set collected from the second run of the LHC. With more data to be recorded from the particle accelerator’s next run and with the High-Luminosity LHC, the ATLAS and CMS collaborations expect to reach the sensitivity (5 sigma) needed to establish the discovery of the Higgs boson decay to two muons and constrain possible theories of physics beyond the Standard Model that would affect this decay mode of the Higgs boson.

    Scientific materials

    Papers:
    CMS physics analysis summary: https://cds.cern.ch/record/2725423
    ATLAS paper on arXiv: https://arxiv.org/abs/2007.07830

    Physics briefings:
    CMS: https://cmsexperiment.web.cern.ch/news/cms-sees-evidence-higgs-boson-decaying-muons
    ATLAS: https://atlas.cern/updates/physics-briefing/new-search-rare-higgs-decays-muons

    Event displays and plots:
    CMS: https://cds.cern.ch/record/2720665?ln=en
    http://cds.cern.ch/record/2725728
    ATLAS: https://cds.cern.ch/record/2725717?ln=en
    https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2019-14

    Images:
    CMS muon system:

    ATLAS muon spectrometer:

    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 Image Claudia Marcelloni CERN/ATLAS


    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

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    SixTRack CERN LHC particles

     
  • richardmitnick 1:40 pm on February 27, 2020 Permalink | Reply
    Tags: "‘Flash photography’ at the LHC", , , CERN CMS, , , , ,   

    From Symmetry: “‘Flash photography’ at the LHC” 

    Symmetry Mag
    From Symmetry<

    02/27/20
    Sarah Charley

    1
    Photo by Tom Bullock

    An extremely fast new detector inside the CMS detector will allow physicists to get a sharper image of particle collisions.

    Some of the best commercially available high-speed cameras can capture thousands of frames every second. They produce startling videos of water balloons popping and hummingbirds flying in ultra-slow motion.

    But what if you want to capture an image of a process so fast that it looks blurry if the shutter is open for even a billionth of a second? This is the type of challenge scientists on experiments like CMS and ATLAS face as they study particle collisions at CERN’s Large Hadron Collider.

    When the LHC is operating to its full potential, bunches of about 100 billion protons cross each other’s paths every 25 nanoseconds. During each crossing, which lasts about 2 nanoseconds, about 50 protons collide and produce new particles. Figuring out which particle came from which collision can be a daunting task.

    “Usually in ATLAS and CMS, we measure the charge, energy and momentum of a particle, and also try to infer where it was produced,” says Karri DiPetrillo, a postdoctoral fellow working on the CMS experiment at the US Department of Energy’s Fermilab. “We’ve had timing measurements before—on the order of nanoseconds, which is sufficient to assign particles to the correct bunch crossing, but not enough to resolve the individual collisions within the same bunch.”

    Thanks to a new type of detector DiPetrillo and her collaborators are building for the CMS experiment, this is about to change.

    CERN/CMS Detector

    Physicists on the CMS experiment are devising a new detector capable of creating a more accurate timestamp for passing particles. The detector will separate the 2-nanosecond bursts of particles into several consecutive snapshots—a feat a bit like taking 30 billion pictures a second.

    This will help physicists with a mounting challenge at the LHC: collision pileup.

    Picking apart which particle tracks came from which collision is a challenge. A planned upgrade to the intensity of the LHC will increase the number of collisions per bunch crossing by a factor of four—that is from 50 to 200 proton collisions—making that challenge even greater.

    Currently, physicists look at where the collisions occurred along the beamline as a way to identify which particular tracks came from which collision. The new timing detector will add another dimension to that.

    “These time stamps will enable us to determine when in time different collisions occurred, effectively separating individual bunch crossings into multiple ‘frames,’” says DiPetrillo.

    DiPetrillo and fellow US scientists working on the project are supported by DOE’s Office of Science, which is also contributing support for the detector development.

    According to DiPetrillo, being able to separate the collisions based on when they occur will have huge downstream impacts on every aspect of the research. “Disentangling different collisions cleans up our understanding of an event so well that we’ll effectively gain three more years of data at the High-Luminosity LHC. This increase in statistics will give us more precise measurements, and more chances to find new particles we’ve never seen before,” she says.

    The precise time stamps will also help physicists search for heavy, slow moving particles they might have missed in the past.

    “Most particles produced at the LHC travel at close to the speed of light,” DiPetrillo says. “But a very heavy particle would travel slower. If we see a particle arriving much later than expected, our timing detector could flag that for us.”

    The new timing detector inside CMS will consist of a 5-meter-long cylindrical barrel made from 160,000 individual scintillating crystals, each approximately the width and length of a matchstick. This crystal barrel will be capped on its open ends with disks containing delicately layered radiation-hard silicon sensors. The barrel, about 2 meters in diameter, will surround the inner detectors that compose CMS’s tracking system closest to the collision point. DiPetrillo and her colleagues are currently working out how the various sensors and electronics at each end of the barrel will coordinate to give a time stamp within 30 to 50 picoseconds.

    “Normally when a particle passes through a detector, the energy it deposits is converted into an electrical pulse that rises steeply and the falls slowly over the course of a few nanoseconds,” says Joel Butler, the Fermilab scientist coordinating this project. “To register one of these passing particles in under 50 picoseconds, we need a signal that reaches its peaks even faster.”

    Scientists can use the steep rising slopes of these signals to separate the collisions not only in space, but also in time. In the barrel of the detector, a particle passing through the crystals will release a burst of light that will be recorded by specialized electronics. Based on when the intense flash of light arrives at each sensor, physicists will be able to calculate the particle’s exact location and when it passed. Particles will also produce a quick pulse in the endcaps, which are made from a new type of silicon sensor that amplifies the signal. Each silicon sensor is about the size of a domino and can determine the location of a passing particle to within 1.3 millimeters.

    The physicists working on the timing detector plan to have all the components ready and installed inside CMS for the start-up of the High Luminosity LHC in 2027

    “High-precision timing is a new concept in high-energy physics,” says DiPetrillo. “I think it will be the direction we pursue for future detectors and colliders because of its huge physics potential. For me, it’s an incredibly exciting and novel project to be on right now.”

    LHC

    CERN map


    CERN LHC Maximilien Brice and Julien Marius Ordan


    CERN LHC particles

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:22 am on January 23, 2020 Permalink | Reply
    Tags: , , CERN CMS, , , , , , ,   

    From Fermi National Accelerator Lab: “USCMS collaboration gets green light on upgrades to CMS particle detector” 

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    January 22, 2020
    Leah Hesla

    In its ongoing quest to understand the nature of the universe’s fundamental constituents, the CMS collaboration has reached another milestone.

    CERN/CMS Detector

    In October 2019, the U.S. contingent of the CMS collaboration presented their plans to upgrade the CMS particle detector for the high-luminosity phase of the Large Hadron Collider at CERN.

    CERN LHC Tunnel

    The upgrades would enable CMS to handle the challenging environment brought on by the upcoming increase in the LHC’s particle collision rate, fully exploiting the discovery potential of the upgraded machine.

    In response, on Dec. 19, 2019, the Department of Energy Office of Science gave the plan its stamp of CD-1 approval, signaling that it favorably evaluated the project’s conceptual design, schedule range and cost, among other factors.

    “This is a major achievement because it paves the way for the next major steps in our project, in which funds are allocated to start the production phase,” said scientist Anadi Canepa, head of the Fermilab CMS Department. “The U.S. project team was extremely satisfied. Preparing for CD-1 was a monumental effort.”

    2
    The CMS detector upgrade team met in October 2019 for a DOE review. Photo: Reidar Hahn, Fermilab

    The LHC’s increase in beam intensity is planned for 2027, when it will become the High-Luminosity LHC. Racing around its 17-mile circumference, the upgraded collider’s proton beams will smash together to reveal even more about the nature of the subatomic realm thanks to a 10-fold increase in collision rate compared to the LHC’s design value.

    The cranked up intensity means that the High-Luminosity LHC will deliver an unprecedented amount of data, and the giant detectors that sit in the path of the beam have to be able to withstand the higher data delivery rate and radiation dose. In preparation, USCMS will upgrade the CMS detector to keep up with the increase in data output, not to mention to harsher collision environment.

    The collaboration plans to upgrade the detector with state-of-the-art technology. The new detector will exhibit improved sensitivity, with over 2 billion sensor channels — up from 80 million. USCMS is also replacing the central part of the detector so that, when charged particles fly through it, the upgraded device will take readings of their momenta at an astounding 40 million times per second, a first for hadron colliders. They’re implementing an innovative design for the detector, measuring the energy of particles using very precise silicon sensors. The upgraded CMS will also have a breakthrough component to take higher-resolution, more precisely timed images of complex particle interactions. Scientists are introducing a system using machine learning on electronic circuits called FPGAs to more efficiently select which of the billions of particle events that CMS processes every 25 nanoseconds might signal new physics.

    “The successful completion of the CD-1 review is a reflection of the competence, commitment and dedication of a very large team of Fermilab scientists and university colleagues,” said Fermilab scientist Steve Nahn, U.S. project manager for the CMS detector upgrade.

    Now USCMS will refine the plan, getting it ready to serve as the project baseline.

    “With these improvements, we’ll be able to explore uncharted territories and might discover new phenomena that revolutionize our description of nature,” Canepa said.

    The USCMS collaboration comprises Fermilab and 54 institutions.

    See the full 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 3:29 pm on January 14, 2020 Permalink | Reply
    Tags: , , CERN CMS, , , Dilepton channel, Drell–Yan process, , , Searching for new physics in the TeV regime by looking for the decays of new particles., The dark photon (Zd)?   

    From CERN Courier: “CMS goes scouting for dark photons” 


    From CERN Courier

    6 December 2019
    A report from the CMS experiment

    One of the best strategies for searching for new physics in the TeV regime is to look for the decays of new particles. The CMS collaboration has searched in the dilepton channel for particles with masses above a few hundred GeV since the start of LHC data taking. Thanks to newly developed triggers, the searches are now being extended to the more difficult lower range of masses. A promising possible addition to the Standard Model (SM) that could exist in this mass range is the dark photon (Zd). Its coupling with SM particles and production rate depend on the value of a kinetic mixing coefficient ε, and the resulting strength of the interaction of the Zd with ordinary matter may be several orders of magnitude weaker than the electroweak interaction.

    The CMS collaboration has recently presented results of a search for a narrow resonance decaying to a pair of muons in the mass range from 11.5 to 200 GeV. This search looks for a strikingly sharp peak on top of a smooth dimuon mass spectrum that arises mainly from the Drell–Yan process. At masses below approximately 40 GeV, conventional triggers are the main limitation for this analysis as the thresholds on the muon transverse momenta (pT), which are applied online to reduce the rate of events saved for offline analysis, introduce a significant kinematic acceptance loss, as evident from the red curve in figure 1.

    1
    Fig. 1. Dimuon invariant-mass distributions obtained from data collected by the standard dimuon triggers (red) and the dimuon scouting triggers (green).

    A dedicated set of high-rate dimuon “scouting” triggers, with some additional kinematic constraints on the dimuon system and significantly lower muon pT thresholds, was deployed during Run 2 to overcome this limitation. Only a minimal amount of high-level information from the online reconstruction is stored for the selected events. The reduced event size allows significantly higher trigger rates, up to two orders of magnitude higher than the standard muon triggers. The green curve in figure 1 shows the dimuon invariant mass distribution obtained from data collected with the scouting triggers. The increase in kinematic acceptance for low masses can be well appreciated.

    The full data sets collected with the muon scouting and standard dimuon triggers during Run 2 are used to probe masses below 45 GeV, and between 45 and 200 GeV, respectively, excluding the mass range from 75 to 110 GeV where Z-boson production dominates. No significant resonant peaks are observed, and limits are set on ε2 at 90% confidence as a function of the ZD mass (figure 2). These are among the world’s most stringent constraints on dark photons in this mass range.

    2
    Fig. 2. Upper limits on ε2 as a function of the ZD mass. Results obtained with data collected by the dimuon scouting triggers are to the left of the dashed line. Constraints from measurement of the electroweak observables are shown in light blue.

    See the full article here .


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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN/ATLAS detector

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

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  • richardmitnick 2:41 pm on October 7, 2019 Permalink | Reply
    Tags: "Watching the top quark mass run", , , CERN CMS, , , ,   

    From CERN CMS: “Watching the top quark mass run” 

    Cern New Bloc

    Cern New Particle Event

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    From CERN CMS

    10.7.19
    CMS Collaboration

    1
    A candidate event for a top quark–antiquark pair recorded by the CMS detector. Such an event is expected to produce an electron (green), a muon (red) of opposite charge, two high-energy “jets” of particles (orange) and a large amount of missing energy (purple) (Image: CMS/CERN)

    For the first time, CMS physicists have investigated an effect called the “running” of the top quark mass, a fundamental quantum effect predicted by the Standard Model.

    Mass is one of the most complex concepts in fundamental physics, which went through a long history of conceptual developments. Mass was first understood in classical mechanics as a measure of inertia and was later interpreted in the theory of special relativity as a form of energy. Mass has a similar meaning in modern quantum field theories that describe the subatomic world. The Standard Model of particle physics is such a quantum field theory, and it can describe the interaction of all known fundamental particles at the energies of the Large Hadron Collider.

    Quantum Chromodynamics is the part of the Standard Model that describes the interactions of fundamental constituents of nuclear matter: quarks and gluons. The strength of the interaction between these particles depends on a fundamental parameter called the strong coupling constant. According to Quantum Chromodynamics, the strong coupling constant rapidly decreases at higher energy scales. This effect is called asymptotic freedom, and the scale evolution is referred to as the “running of the coupling constant.” The same is also true for the masses of the quarks, which can themselves be understood as fundamental couplings, for example, in connection with the interaction with the Higgs field. In Quantum Chromodynamics, the running of the strong coupling constant and of the quark masses can be predicted, and these predictions can be experimentally tested.

    The experimental verification of the running mass is an essential test of the validity of Quantum Chromodynamics. At the energies probed by the Large Hadron Collider, the effects of physics beyond the Standard Model could lead to modifications of the running of mass. Therefore, a measurement of this effect is also a search for unknown physics. Over the past decades, the running of the strong coupling constant has been experimentally verified for a wide range of scales. Also, evidence was found for the running of the masses of the charm and beauty quarks.

    2
    Figure 1: Display of an LHC collision detected by the CMS detector that contains a reconstructed top quark-antiquark pair. The display shows an electron (green) and a muon (red) of opposite charge, two highly energetic jets (orange) and a large amount of missing energy (purple).

    With a new measurement, the CMS Collaboration investigates for the first time the running of the mass of the heaviest of the quarks: the top quark. The production rate of top quark pairs (a quantity that depends on the top quark mass) was measured at different energy scales. From this measurement, the top quark mass is extracted at those energy scales using theory predictions that predict the rate at which top quark-antiquark pairs are produced.

    3
    Figure 2: The running of the top quark mass determined from the data (black points) compared to the theoretical prediction (red line). As the absolute scale of the top quark mass is not relevant for this measurement, the values have been normalised to the second data point.

    Experimentally, interesting top quark pair collisions are selected by searching for the specific decay products of a top quark-antiquark pair. In the overwhelming majority of cases, top quarks decay into an energetic jet and a W boson, which in turn can decay into a lepton and a neutrino. Jets and leptons can be identified and measured with high precision by the CMS detector, while neutrinos escape undetected and reveal themselves as missing energy. A collision that is likely the production of a top quark-antiquark pair as it is seen in the CMS detector is shown in Figure 1. Such a collision is expected to contain an electron, a muon, two energetic jets, and a large amount of missing energy.

    The measured running of the top quark mass is shown in Figure 2. The markers correspond to the measured points, while the red line represents the theoretical prediction according to Quantum Chromodynamics. The result provides the first indication of the validity of the fundamental quantum effect of the running of the top quark mass and opens a new window to test our understanding of the strong interaction. While a lot more data will be collected in the future LHC runs starting with Run 3 in 2021, this particular CMS result is mostly sensitive to uncertainties coming from the theoretical knowledge of the top quark in Quantum Chromodynamics. To witness the top quark mass running with even higher precision and maybe unveil signs of new physics, theory developments and experimental efforts will both be necessary. In the meantime, watch the top quark run!

    See the full article here.


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  • richardmitnick 3:30 pm on September 17, 2019 Permalink | Reply
    Tags: "LS2 Report: CMS set to glitter with installation of new GEMs", , CERN CMS, GEMs-Gas Electron Multipliers, , , ,   

    From CERN CMS: “LS2 Report: CMS set to glitter with installation of new GEMs” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    From CERN CMS

    17 September, 2019
    Achintya Rao

    1
    The GEMs being installed in CMS (Image: Maximilien Brice/CERN)

    Muons – heavy, weakly interacting particles – zip past the inner layers of the Compact Muon Solenoid (CMS), after being produced in collisions by the Large Hadron Collider (LHC). They are observed using special detectors placed on the periphery of the cylindrical device, where they are the particles most likely to register a signal. Although CMS, as the name suggests, was designed with the ability to observe with high precision nearly every muon produced within it, it will become more challenging to do so in a few years’ time. The High-Luminosity LHC (HL-LHC) will begin operations in 2026, providing on average over five times more simultaneous proton–proton collisions than before. Various components of CMS, including the muon system, are being upgraded during the ongoing second long shutdown (LS2) of CERN’s accelerator complex, in order to cope with the HL-LHC’s higher data rates.

    Muon detectors contain different mixtures of gases that get ionised when high-energy muons fly through them, providing information about where the muon was at a given instant. The CMS muon system has so far used three different types of detectors: Drift Tubes (DT), Cathode Strip Chambers (CSC) and Resistive Plate Chambers (RPC). Around a decade ago, at about the time that CMS began collecting LHC collision data, it was decided to build a completely new type of detector called Gas Electron Multipliers, or GEM, to improve the muon-detection abilities of CMS in the HL-LHC era. After extensive R&D, the first GEMs were assembled and tested at CERN’s Prévessin site in a dedicated fabrication facility. In July, two of 72 so-called “superchambers” of GEMs were transported carefully to Point 5 and installed within CMS. Each superchamber had a bottle of gas strapped on top of it on the trolley so the detector could keep “breathing” the inert air. The remaining 70 superchambers will be installed later in LS2.

    “The GEMs are new technology for CMS and Run 3 of the LHC will give us the opportunity to evaluate their performance,” says Archana Sharma, who has led the CMS-GEM team since 2009. “Of course,” she continues, “it’s not only there to be tested. The first GEMs will work with the existing CSCs to provide valuable triggering information to select the most interesting collision events.” Two more GEM stations with 288 and 216 modules respectively will be definitively installed in the coming years, in time for the HL-LHC.

    The muon-system team have been busy upgrading the electronics of the 180 CSCs located closest to the beam line to prepare for the HL-LHC. “We have already removed, refurbished and reinstalled 54 CSCs this year,” notes Anna Colaleo, CMS muon-system manager. “Work on replacing the electronics for another batch of CSCs is in progress and we plan on completing this endeavour by the summer of 2020.”


    A timelapse showing the extraction of CSCs from the CMS endcap and their transport to the refurbishment area on the surface (Video: CMS/CERN)

    CMS is also performing critical maintenance on the rest of the muon detectors during LS2. As expected, over the course of several years of operation, some components of these detectors have deteriorated slightly. The RPCs have been made more airtight to reduce gas leaks, while both DTs and RPCs have had some broken components replaced. In addition, neutron shielding is being added to the top of the DTs located in the central barrel to protect CMS from the neutron background caused by the particle beam interacting with the beam pipe.

    With nearly a year and a half of LS2 left, the CMS experiment site at LHC Point 5 continues to be a hub of activity as the collaboration prepares for the LHC’s Run 3 and beyond.

    See the full article here.


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  • richardmitnick 9:36 am on August 29, 2019 Permalink | Reply
    Tags: "From capturing collisions to avoiding them", , , CERN CMS, , , ,   

    From CERN: “From capturing collisions to avoiding them” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    29 August, 2019
    Kate Kahle

    1
    Around 100 simultaneous proton–proton collisions in an event recorded by the CMS experiment (Image: Thomas McCauley/CMS/CERN)

    With about one billion proton–proton collisions per second at the Large Hadron Collider (LHC), the LHC experiments need to sift quickly through the wealth of data to choose which collisions to analyse. To cope with an even higher number of collisions per second in the future, scientists are investigating computing methods such as machine-learning techniques. A new collaboration is now looking at how these techniques deployed on chips known as field-programmable gate arrays (FPGAs) could apply to autonomous driving, so that the fast decision-making used for particle collisions could help prevent collisions on the road.

    FPGAs have been used at CERN for many years and for many applications. Unlike the central processing unit of a laptop, these chips follow simple instructions and process many parallel tasks at once. With up to 100 high-speed serial links, they are able to support high-bandwidth inputs and outputs. Their parallel processing and re-programmability make them suitable for machine-learning applications.

    2
    An FPGA-based readout card for the CMS tracker (Image: John Coughlan/CMS/CERN)

    The challenge, however, has been to fit complex deep-learning algorithms – a particular class of machine-learning algorithms – in chips of limited capacity. This required software developed for the CERN-based experiments, called “hls4ml”, which reduces the algorithms and produces FPGA-ready code without loss of accuracy or performance, allowing the chips to execute decision-making algorithms in micro-seconds.

    A new collaboration between CERN and Zenuity, the autonomous driving software company headquartered in Sweden, plans to use the techniques and software developed for the experiments at CERN to research their use in deploying deep learning on FPGAs, a particular class of machine-learning algorithms, for autonomous driving. Instead of particle-physics data, the FPGAs will be used to interpret huge quantities of data generated by normal driving conditions, using readouts from car sensors to identify pedestrians and vehicles. The technology should enable automated drive cars to make faster and better decisions and predictions, thus avoiding traffic collisions.

    To find out more about CERN technologies and their potential applications, visit kt.cern/technologies.

    See the full article here.


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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS


    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN map

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  • richardmitnick 2:42 pm on August 26, 2019 Permalink | Reply
    Tags: , CERN CMS, , , , ,   

    From Fermi National Accelerator Lab: “USCMS completes phase 1 upgrade program for CMS detector at CERN” 

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    August 26, 2019
    James Wetzel

    The CMS experiment at CERN’s Large Hadron Collider has achieved yet another significant milestone in its already storied history as a leader in the field of high-energy experimental particle physics.

    The U.S. contingent of the CMS collaboration, known as USCMS and managed by Fermilab, has been granted the Department of Energy’s final Critical Decision- 4 approval for its multiyear Phase 1 Detector Upgrade program, formally signifying the completion of the project after having met every stated goal — on time and under budget.

    “Getting CD-4 approval is a tremendous vote of confidence for the many people involved in CMS,” said Fermilab scientist Steve Nahn, U.S. project manager for the CMS detector upgrade. “The LHC is the best tool we have for further explication of the particle nature of the universe, and there are still mysteries to solve, so we have to have the best apparatus we can to continue the exploration.”

    LHC

    CERN map


    CERN LHC Maximilien Brice and Julien Marius Ordan


    CERN LHC particles

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    The CMS experiment is a generation-spanning effort to build, operate and upgrade a particle-detecting behemoth that observes its protean prey in a large but cramped cavern 300 feet beneath the French countryside. CMS is one of four large experiments situated along the LHC accelerator complex, operated by CERN in Geneva, Switzerland. The LHC is a 17-mile-round ring of magnets that accelerates two beams of protons in opposite directions, each to 99.999999999% the speed of light, and forces them to collide at the centers of CMS and the LHC’s other experiments: ALICE, LHCb and ATLAS.

    1
    Fermilab scientists Nadja Strobbe and Jim Hirschauer test chips for the CMS detector upgrades. Photo: Reidar Hahn

    The main goal of CMS (and the other LHC experiments) is to keep track of which particles emerge from the rapture of pure energy created from the collisions in order to search for new particles and phenomena. In catching sight of such new phenomena, scientists aim to answer some of the most fundamental questions we have about how the universe works.

    The global CMS collaboration comprises more than 5,000 professionals — including roughly 1,000 students — from over 200 institutes and universities across more than 50 countries. This international team collaborates to design, build, commission and operate the CMS detector, whose data is then distributed to dedicated centers in 40 nations for analysis. And analysis is their raison d’etre. By sussing out patterns in the data, CMS scientists search for previously unseen or unconfirmed phenomena and measure the properties of elementary particles that make up the universe with greater precision. To date, CMS has published over 900 papers.

    The USCMS collaboration is the single largest national group in CMS, involving 51 American universities and institutions in 24 states and Puerto Rico, over 400 Ph.D. physicists, and more than 200 graduate students and other professionals. USCMS has played a primary role in much of the CMS experiment’s original design and construction, including a wide network of eight CMS computing centers located across the United States, and in the experiment’s data analysis. USCMS is supported by the U.S. Department of Energy and the National Science Foundation and has played an integral role in the success of the CMS collaboration as a whole from its founding.

    The CMS experiment, the LHC and the other LHC experiments became operational in 2009 (17 years after the CMS letter of intent), beginning a 10-year data-taking period referred to as Phase 1.

    Phase 1 was divided into four major epochs, alternating two periods of data-taking with two periods of maintenance and upgrade operations. The two data-taking periods are referred to as Run 1 (2009-2013) and Run 2 (2015-2018). It was during Run 1 (in 2012) that the CMS and ATLAS collaborations jointly announced they each had observed the long predicted Higgs boson, resulting in a Nobel Prize awarded a year later to scientists Peter Higgs and François Englert, and a further testament to the strength of the Standard Model of particle physics, the theory within which the Higgs boson was first hypothesized in 1964.

    Peter Higgs

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    “That prize was a historic triumph of every individual, institution and nation involved with the LHC project, not only validating the Higgs conjecture, a cornerstone of the Standard Model, but also giving science a new particle to use as a tool for further exploration,” Nahn said. “This discovery and every milestone CMS has achieved since then is encouragement to continue working toward further discovery. That goes for our latest approval milestone.”

    Standard Model of Particle Physics

    2
    Fermilab scientist Maral Alyari and Stephanie Timpone conduct CMS pixel detector work. Photo: Reidar Hahn

    During the entirety of Phase 1, the wizard-like LHC particle accelerator experts were continually ramping up the collision energy and intensity, or in particle physics parlance, the luminosity of the LHC beam. The CMS technical team was charged with fulfilling the Phase 1 Upgrade plan, a series of hardware upgrades to the detector that allowed it to fully profit from the gains the LHC team was providing.

    While the LHC accelerator folks were prepping to push 20 times as many particles through the experiments per second, the experiments were busy upgrading their systems to handle this major influx of particles and the resulting data. This meant updating many of the readout electronics with faster and more capable brains to manage and process the data produced by CMS.

    With support from the Department of Energy’s Office of Science and the National Science Foundation, USCMS implemented $40 million worth of these strategic upgrades on time and under budget.

    With these upgrades complete, the CMS detector is now ready for LHC Run 3, which will go from 2021-23, and the collaboration is starting the stage of data taking on a solid foundation.

    Still, USCMS isn’t taking a break: The collaboration is already gearing up for its next, even more ambitious set of upgrades, planned for installation after Run 3. This USCMS upgrade phase will prepare the detector for an even higher luminosity, resulting in a data set 10 times greater than what the LHC provides currently.

    Every advance in the CMS detector ensures that it will support the experiment through 2038, when the LHC is planned to complete its final run.

    “For the last decade, we’ve worked to improve and enhance the CMS detector to squeeze everything we can out of the LHC’s collisions,” Nahn said. “We’re prepared to do the same for the next two decades to come.”

    See the full here.


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    FNAL Icon

    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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