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  • richardmitnick 12:04 pm on May 14, 2019 Permalink | Reply
    Tags: >Model-dependent vs model-independent research, , , CERN CMS, , , , , , , ,   

    From Symmetry: “Casting a wide net” 

    Symmetry Mag
    From Symmetry

    05/14/19
    Jim Daley

    1
    Illustration by Sandbox Studio, Chicago

    In their quest to discover physics beyond the Standard Model, physicists weigh the pros and cons of different search strategies.

    On October 30, 1975, theorists John Ellis, Mary K. Gaillard and D.V. Nanopoulos published a paper [Science Direct] titled “A Phenomenological Profile of the Higgs Boson.” They ended their paper with a note to their fellow scientists.

    “We should perhaps finish with an apology and a caution,” it said. “We apologize to experimentalists for having no idea what is the mass of the Higgs boson… and for not being sure of its couplings to other particles, except that they are probably all very small.

    “For these reasons, we do not want to encourage big experimental searches for the Higgs boson, but we do feel that people performing experiments vulnerable to the Higgs boson should know how it may turn up.”

    What the theorists were cautioning against was a model-dependent search, a search for a particle predicted by a certain model—in this case, the Standard Model of particle physics.

    Standard Model of Particle Physics

    It shouldn’t have been too much of a worry. Around then, most particle physicists’ experiments were general searches, not based on predictions from a particular model, says Jonathan Feng, a theoretical particle physicist at the University of California, Irvine.

    Using early particle colliders, physicists smashed electrons and protons together at high energies and looked to see what came out. Samuel Ting and Burton Richter, who shared the 1976 Nobel Prize in physics for the discovery of the charm quark, for example, were not looking for the particle with any theoretical prejudice, Feng says.

    That began to change in the 1980s and ’90s. That’s when physicists began exploring elegant new theories such as supersymmetry, which could tie up many of the Standard Model’s theoretical loose ends—and which predict the existence of a whole slew of new particles for scientists to try to find.

    Of course, there was also the Higgs boson. Even though scientists didn’t have a good prediction of its mass, they had good motivations for thinking it was out there waiting to be discovered.

    And it was. Almost 40 years after the theorists’ tongue-in-cheek warning about searching for the Higgs, Ellis found himself sitting in the main auditorium at CERN next to experimentalist Fabiola Gianotti, the spokesperson of the ATLAS experiment at the Large Hadron Collider who, along with CMS spokesperson Joseph Incandela, had just co-announced the discovery of the particle he had once so pessimistically described.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    Model-dependent vs model-independent

    Scientists’ searches for particles predicted by certain models continue, but in recent years, searches for new physics independent of those models have begun to enjoy a resurgence as well.

    “A model-independent search is supposed to distill the essence from a whole bunch of specific models and look for something that’s independent of the details,” Feng says. The goal is to find an interesting common feature of those models, he explains. “And then I’m going to just look for that phenomenon, irrespective of the details.”

    Particle physicist Sara Alderweireldt uses model-independent searches in her work on the ATLAS experiment at the Large Hadron Collider.

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    Alderweireldt says that while many high-energy particle physics experiments are designed to make very precise measurements of a specific aspect of the Standard Model, a model-independent search allows physicists to take a wider view and search more generally for new particles or interactions. “Instead of zooming in, we try to look in as many places as possible in a consistent way.”

    Such a search makes room for the unexpected, she says. “You’re not dependent on the prior interpretation of something you would be looking for.”

    Theorist Patrick Fox and experimentalist Anadi Canepa, both at Fermilab, collaborate on searches for new physics.


    In Canepa’s work on the CMS experiment, the other general-purpose particle detector at the LHC, many of the searches are model-independent.

    While the nature of these searches allows them to “cast a wider net,” Fox says, “they are in some sense shallower, because they don’t manage to strongly constrain any one particular model.”

    At the same time, “by combining the results from many independent searches, we are getting closer to one dedicated search,” Canepa says. “Developing both model-dependent and model-independent searches is the approach adopted by the CMS and ATLAS experiments to fully exploit the unprecedented potential of the LHC.”

    Driven by data and powered by machine learning

    Model-dependent searches focus on a single assumption or look for evidence of a specific final state following an experimental particle collision. Model-independent searches are far broader—and how broad is largely driven by the speed at which data can be processed.

    “We have better particle detectors, and more advanced algorithms and statistical tools that are enabling us to understand searches in broader terms,” Canepa says.

    One reason model-independent searches are gaining prominence is because now there is enough data to support them. Particle detectors are recording vast quantities of information, and modern computers can run simulations faster than ever before, she says. “We are able to do model-independent searches because we are able to better understand much larger amounts of data and extreme regions of parameter and phase space.”

    Machine-learning is a key part of this processing power, Canepa says. “That’s really a change of paradigm, because it really made us make a major leap forward in terms of sensitivity [to new signals]. It really allows us to benefit from understanding the correlations that we didn’t capture in a more classical approach.”

    These broader searches are an important part of modern particle physics research, Fox says.

    “At a very basic level, our job is to bequeath to our descendants a better understanding of nature than we got from our ancestors,” he says. “One way to do that is to produce lots of information that will stand the test of time, and one way of doing that is with model-independent searches.”

    Models go in and out of fashion, he adds. “But model-independent searches don’t feel like they will.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 2:12 pm on March 22, 2019 Permalink | Reply
    Tags: , , CERN CMS, , Muoscope-a new small-scale portable muon telescope, , ,   

    From CERN CMS: “A ‘muoscope’ with CMS technology” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    From CERN CMS

    22 March, 2019
    Cristina Agrigoroae

    1
    The resistive plate chambers (RPC) at CMS are fast gaseous detectors that provide a muon trigger system (Image: CERN)

    Particle physicists are experts at seeing invisible things and their detecting techniques have already found many applications in medical imaging or the analysis of art works. Researchers from the CMS experiment at the Large Hadron Collider are developing a new application based on one of the experiment’s particle detectors: a new, small-scale, portable muon telescope, which will allow imaging of visually inaccessible spaces.

    CERN CMS Muoscope- a new, small-scale, portable muon telescope developed by the CMS Collaborators from Ghent University and the University of Louvain in Belgium

    Earth’s atmosphere is constantly bombarded by particles arriving from outer space. By interacting with atmospheric matter, they decay into a cascade of new particles, generating a flux of muons, heavier cousins of electrons. These cosmic-ray muons continue their journey towards the Earth’s surface, travelling through almost all material objects.

    This “superpower” of muons makes them the perfect partners for seeing through thick walls or other visually challenging subjects. Volcanic eruptions, enigmatic ancient pyramids, underground caves and tunnels: these can all be scanned and explored from the inside using muography, an imaging method using naturally occurring background radiation in the form of cosmic-ray muons.

    Large-area muon telescopes have been developed in recent years for many different applications, some of which use technology developed for the LHC detectors. The muon telescope conceived by CMS researchers from two Belgian universities, Ghent University and the Catholic University of Louvain, is compact and light and therefore easy to transport. It is nonetheless able to perform muography at high resolution. It will be the first spin-off for muography using the CMS Resistive Plate Chambers (RPC) technology. A first prototype of the telescope, also baptised a “muoscope”, has been built with four RPC planes with an active area of 16×16 cm. The same prototype was used in the “UCL to Mars” project; it was tested for its robustness in a simulation of Mars-like conditions in the Utah Desert, where it operated for one month and later came back fully functional.

    Other CMS technologies have been used in muon tomography for security and environmental protection, as well as for homeland security.

    Learn more about the muon telescope here.

    See the full article here.


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  • richardmitnick 3:26 pm on February 26, 2019 Permalink | Reply
    Tags: "What’s in store for the CMS detector over the next two years?", , CERN CMS, , , , ,   

    From CERN CMS: “What’s in store for the CMS detector over the next two years?” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    From CERN CMS

    26 February, 2019
    Letizia Diamante

    CERN/CMS Detector

    A jewel of particle physics, the CMS experiment is a 14 000-tonne detector that aims to solve a wide range of questions about the mysteries around the Higgs boson and dark matter.

    CERN CMS Higgs Event

    Now that the Large Hadron Collider (LHC) beam has been switched off for a two-year technical stop, Long Shutdown 2 (LS2), CMS is preparing for significant maintenance work and upgrades.

    1
    This diagram of the CMS detector shows some of the maintenance and upgrades in store over the next years

    All the LHC experiments at CERN want to exploit the full benefits of the accelerator’s upgrade, the High-Luminosity LHC (HL-LHC), scheduled to start in 2026.

    The HL-LHC will produce between five and ten times more collisions than the LHC, allowing more precision measurements of rare phenomena that are predicted in the Standard Model to be taken, and maybe even detecting new particles that have never been seen before. To take advantage of this, some of CMS’s components need to be replaced.

    Standard Moldel of Particle Physics

    Standard Model of Particle Physics from Symmetry Magazine

    In the heart of CMS

    Hidden inside several layers of subdetectors, the pixel detector surrounding the beam pipe is the core of the experiment, as it is the closest to the particle-collision point. During LS2, the innermost layer of the present pixel detector will be replaced, using more high-luminosity-tolerant and radiation-tolerant components. The beam pipe will also be replaced in LS2, with one that will allow the extremities of the future pixel detectors to get even closer to the interaction point. This third-generation pixel detector will be installed during the third long shutdown (LS3) in 2024–2026.

    4
    CMS core removal during the Long Shutdown 2 (LS2) (Image: Maximilien Brice/Julien Ordan/CERN)

    Without missing a thing

    Beyond the core, the CMS collaboration is also planning to work on the outermost part of the detector, which detects and measures muons – particles similar to electrons, but much heavier. They are preparing to install 40 large Multi-Gas Electron Multiplier (GEM) chambers to measure muons that scatter at an angle of around 10° – one of the most challenging angles for the detector to deal with. Invented in 1997 by Fabio Sauli, GEM chambers are already used in other CERN experiments, including COMPASS, TOTEM and LHCb, but the scale of CMS is far greater than the other detectors. The GEM chambers consist of a thin, metal-clad polymer foil, chemically pierced with millions of holes, typically 50 to 100 per millimetre, submerged in a gas. As muons pass through, electrons released by the gas drift into the holes, multiply in a very strong electric field and transfer to a collection region.

    Fast-forward to the future

    Some of the existing detectors would not perform well enough during the HL-LHC phase, as the number of proton–proton collisions produced in the HL-LHC will be ten times higher than that originally planned for the CMS experiment. Therefore, the high-granularity calorimeter (HGCAL) will replace the existing endcap electromagnetic and hadronic calorimeters during LS3, between 2024 and 2026. The new detector will comprise over 1000 m² of hexagonal silicon sensors and plastic scintillator tiles, distributed over 100 layers (50 in each endcap), providing unprecedented information about electrons, photons and hadrons. Exploiting this detector is a major challenge for software and analysis, and physicists and computer science experts are already working on advanced techniques, such as machine learning.

    4
    Ongoing tests on the modules of the high-granularity calorimeter (HGCAL). Intense R&D is planned for LS2 to ensure that the new detector will be ready for installation during LS3. (Image: Maximilien Brice/CERN)

    Building, building, building

    CMS has also been involved with the HL-LHC civil-engineering work, which kick-started in June 2018 and is ongoing. The project includes five new buildings on the surface at Cessy, France, as well as modifications to the underground cavern and galleries.

    CMS’s ambitious plan for the near and longer-term future is preparing the detector for more exciting undertakings. Stay tuned for more.

    Read more in “CMS has high luminosity in sight” in the latest CERN Courier, as well as LS2 highlights from ALICE, ATLAS and LHCb.

    See the full article here.


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    Meet CERN in a variety of places:

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  • richardmitnick 8:42 pm on February 15, 2019 Permalink | Reply
    Tags: , , CERN CMS, , , ,   

    From CERN CMS: “CMS gets first result using largest ever LHC data sample” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    From CERN CMS

    15 February, 2019

    The CMS collaboration at CERN has submitted its first paper based on the full LHC dataset collected in 2018 and data collected in 2016 and 2017.

    Just under three months after the final proton–proton collisions from the Large Hadron Collider (LHC)’s second run (Run 2), the CMS collaboration has submitted its first paper [Physical Review Letters] based on the full LHC dataset collected in 2018 – the largest sample ever collected at the LHC – and data collected in 2016 and 2017. The findings reflect an immense achievement, as a complex chain of data reconstruction and calibration was necessary to be able to use the data for analysis suitable for a scientific result.

    “It is truly a sign of effective scientific collaboration and the high quality of the detector, software and the CMS collaboration as a whole. I am proud and extremely impressed that the understanding of the so recently collected data is sufficiently advanced to produce this very competitive and exciting result,” said CMS spokesperson Roberto Carlin.

    Quantum chromodynamics (QCD) is one of the pillars of the Standard Model of elementary particles and describes how quarks and gluons are confined within composite particles called hadrons, of which protons and neutrons are examples.

    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.

    However, the QCD processes behind this confinement are not yet well understood, despite much progress in the last two decades. One way to understand these processes is to study the little known Bc particle family, which consists of hadrons composed of a beauty quark and a charm antiquark (or vice-versa).

    The high collision energies and rates provided by the Large Hadron Collider opened the path for the exploration of the Bc family. The first studies were published in 2014 [Physical Review Letters] by the ATLAS collaboration, using data collected during LHC’s first run. At the time, ATLAS reported the observation of a Bc particle called Bc(2S). On the other hand, the LHCb collaboration reported in 2017 that their data showed no evidence of Bc(2S) at all. Analysing the large LHC Run 2 data sample, collected in 2016, 2017 and 2018, CMS has now observed Bc(2S) as well as another Bc particle known as Bc*(2S). The collaboration has also been able to measure the mass of Bc(2S) with a good precision. These measurements provide a rich source of information on the QCD processes that bind heavy quarks into hadrons. For more information about the results visit the CMS webpage.

    The results presented at CERN this week.

    See the full article here.


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    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN map

    CERN LHC Grand Tunnel

    CERN LHC particles

     
  • richardmitnick 12:30 pm on November 1, 2018 Permalink | Reply
    Tags: , , CERN CMS, , , , , , Tantalising 'Bumps' in Large Hadron Collider Data   

    From Science Alert: “CERN’s About to Release Details on Tantalising ‘Bumps’ in Large Hadron Collider Data” 

    ScienceAlert

    From Science Alert

    1 NOV 2018
    MICHELLE STARR

    Strap yourselves in, because CERN has something up its sleeve.

    On Thursday 1 November, Large Hadron Collider (LHC) physicists will be discussing the fact that they may have found a new and unexpected new particle.

    “I’d say theorists are excited and experimentalists are very sceptical,” CERN physicist Alexandre Nikitenko told The Guardian. “As a physicist I must be very critical, but as the author of this analysis I must have some optimism too.”

    The telltale signal is a bump in the data collected by the LHC’s Compact Muon Solenoid (CMS) detector as the researchers were smashing together particles to look for something else entirely.

    CERN/CMS Detector

    When heavy particles – such as the Higgs Boson – are produced through particle collisions, they decay almost immediately. This produces a shower of smaller mass particles, as well as increased momentum, which can be picked up by the LHC’s detectors.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    When these particle showers produced pairs of muons (a type of elementary particle that is similar to an electron but with a much higher mass), the team sat up and paid attention. But what they traced these pairs back to was, to be very scientific about it, mega weird.

    The new and unknown particle that seems to have produced the muons has a mass of around 28 GeV (giga-electronvolts), just over a fifth of the mass of the Higgs boson (125 GeV).

    There’s nothing in any of the current models that predicts this mass.

    It’s unlikely to be physics-breaking, sorry to disappoint. But it is strange – a mass that has formed where no mass was expected.

    A word of caution, though: it’s too early to get excited.

    The signal could just be a glitch in the data, generated from random noise, which ended up being the case with what had been a tremendously exciting 750 GeV signal in 2016 – until it was found to be just a statistical fluctuation.

    Until this data has been checked against newer CMS data, as well as data from the ATLAS detector, the discovery remains unconfirmed.

    CERN/ATLAS detector

    Still, an anomalous detection is always interesting – so we’ll be tuning in tomorrow to see what the research team has to say when they give their talk.

    You can also check out their paper – which has yet to be peer-reviewed – on pre-print resource arXiv.

    See the full article here .


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  • richardmitnick 1:10 pm on August 31, 2018 Permalink | Reply
    Tags: , , CERN CMS, , , Hunting for dark quarks, , ,   

    From CERN: “Hunting for dark quarks” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    From CERN

    31 Aug 2018
    Ana Lopes

    1
    A proton–proton collision event with two emerging-jet candidates. (Image: CMS/CERN)

    Quarks are the smallest particles that we know of. In fact, according to the Standard Model of particle physics, which describes all known particles and their interactions, quarks should be infinitely small.

    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

    If that’s not mind-boggling enough, enter dark quarks – hypothetical particles that have been proposed to explain dark matter, an invisible form of matter that fills the universe and holds the Milky Way and other galaxies together.

    In a recent study, the CMS collaboration describes how it has sifted through data from the Large Hadron Collider (LHC) to try and spot dark quarks. Although the search came up empty-handed, it allowed the team to inch closer to the parent particles from which dark quarks may originate.

    One compelling theory extends the Standard Model to explain why the observed mass densities of normal matter and dark matter are similar. It does so by invoking the existence of dark quarks that interact with ordinary quarks via a mediator particle. If such mediator particles were produced in pairs in a proton–proton collision, each mediator particle of the pair would transform into a normal quark and a dark quark, both of which would produce a spray, or “jet”, of particles called hadrons, composed of quarks or dark quarks. In total, there would be two jets of regular hadrons originating from the collision point, and two “emerging” jets that would emerge a distance away from the collision point because dark hadrons would take some time to decay into visible particles.

    In their study, the CMS researchers looked through data from proton–proton collisions collected at the LHC at an energy of 13 TeV to search for instances, or “events”, in which such mediator particles and associated emerging jets might occur. They used two distinguishing features to identify emerging jets and pick them out from a background of events that are expected to mimic their traits.

    The team found no strong evidence for the existence of such emerging jets, but the data allowed them to exclude masses for the hypothetical mediator particle of 400–1250 GeV for dark pions that travel for lengths between 5 and 225 mm before they decay. The results are the first from a dedicated search for such mediator particles and jets.

    See the full article here.


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    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN map

    CERN LHC Grand Tunnel

    CERN LHC particles

    OTHER PROJECTS AT CERN

    CERN AEGIS

    CERN ALPHA

    CERN ALPHA

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    CERN CAST

    CERN CAST Axion Solar Telescope

    CERN CLOUD

    CERN CLOUD

    CERN COMPASS

    CERN COMPASS

    CERN DIRAC

    CERN DIRAC

    CERN ISOLDE

    CERN ISOLDE

    CERN LHCf

    CERN LHCf

    CERN NA62

    CERN NA62

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    CERN TOTEM

    CERN UA9

    CERN Proto Dune

    CERN Proto Dune

     
  • richardmitnick 10:33 am on August 28, 2018 Permalink | Reply
    Tags: , , , CERN CMS, , Long-sought decay of Higgs boson observed, , ,   

    From CERN via phys.org: “Long-sought decay of Higgs boson observed” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    From CERN

    via

    phys.org

    August 28, 2018, CERN

    1
    A candidate event display for the production of a Higgs boson decaying to two b-quarks (blue cones), in association with a W boson decaying to a muon (red) and a neutrino. The neutrino leaves the detector unseen, and is reconstructed through the missing transverse energy (dashed line). Credit: ATLAS Collaboration/CERN

    CERN ATLAS Higgs Event


    CERN ATLAS

    Six years after its discovery, the Higgs boson has at last been observed decaying to fundamental particles known as bottom quarks. The finding, presented today at CERN1 by the ATLAS and CMS collaborations at the Large Hadron Collider (LHC), is consistent with the hypothesis that the all-pervading quantum field behind the Higgs boson also gives mass to the bottom quark. Both teams have submitted their results for publication today.

    CERN CMS Higgs Event


    CERN/CMS Detector

    The Standard Model of particle physics predicts that about 60% of the time a Higgs boson will decay to a pair of bottom quarks, the second-heaviest of the six flavours of quarks.

    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

    Testing this prediction is crucial because the result would either lend support to the Standard Model – which is built upon the idea that the Higgs field endows quarks and other fundamental particles with mass – or rock its foundations and point to new physics.

    Spotting this common Higgs-boson decay channel is anything but easy, as the six-year period since the discovery of the boson has shown. The reason for the difficulty is that there are many other ways of producing bottom quarks in proton–proton collisions. This makes it hard to isolate the Higgs-boson decay signal from the background “noise” associated with such processes. By contrast, the less-common Higgs-boson decay channels that were observed at the time of discovery of the particle, such as the decay to a pair of photons, are much easier to extract from the background.

    To extract the signal, the ATLAS and CMS collaborations each combined data from the first and second runs of the LHC, which involved collisions at energies of 7, 8 and 13 TeV. They then applied complex analysis methods to the data. The upshot, for both ATLAS and CMS, was the detection of the decay of the Higgs boson to a pair of bottom quarks with a significance that exceeds 5 standard deviations. Furthermore, both teams measured a rate for the decay that is consistent with the Standard Model prediction, within the current precision of the measurement.

    2
    Candidate event display for the production of a Higgs boson decaying to two b-quarks. A 2 b-tag, 2-jet, 2-electron event within the signal-like portion of the high pTV and high BDTVH output distribution is shown (Run 337215, Event 1906922941). Electrons are shown as blue tracks with a large energy deposit in the electromagnetic calorimeter, corresponding to light green bars. Two of them form an invariant mass of 93.6 GeV, compatible with a Z boson. The two central high-pT b-tagged jets are represented by light blue cones. They contain the green and yellow bars corresponding to the energy deposition in the electromagnetic and hadronic calorimeters respectively, and they have an invariant mass of 128.1 GeV. The value of pTV is 246.7 GeV, and BDTVH output value is 0.47. Credit: ATLAS Collaboration/CERN

    “This observation is a milestone in the exploration of the Higgs boson. It shows that the ATLAS and CMS experiments have achieved deep understanding of their data and a control of backgrounds that surpasses expectations. ATLAS has now observed all couplings of the Higgs boson to the heavy quarks and leptons of the third generation as well as all major production modes,” said Karl Jakobs, spokesperson of the ATLAS collaboration.

    “Since the first single-experiment observation of the Higgs boson decay to tau-leptons one year ago, CMS, along with our colleagues in ATLAS, has observed the coupling of the Higgs boson to the heaviest fermions: the tau, the top quark, and now the bottom quark. The superb LHC performance and modern machine-learning techniques allowed us to achieve this result earlier than expected,” said Joel Butler, spokesperson of the CMS collaboration.

    With more data, the collaborations will improve the precision of these and other measurements and probe the decay of the Higgs boson into a pair of much-less-massive fermions called muons, always watching for deviations in the data that could point to physics beyond the Standard Model.

    3
    Candidate event display for the production of a Higgs boson decaying to two b-quarks. A 2-tag, 2-jet, 0-lepton event within the signal-like portion of the high pTV and high BDTVH output (Run 339500, Event 694513952) is shown. The ETMiss, shown as a white dashed line, has a magnitude of 479.1 GeV. The two central high-pT b-tagged jets are represented by light blue cones. They contain the green and yellow bars corresponding to the energy deposition in the electromagnetic and hadronic calorimeters respectively. The dijet invariant mass of 128.1 GeV. The BDTVH output value is 0.74. Credit: ATLAS Collaboration/CERN

    “The experiments continue to home in on the Higgs particle, which is often considered a portal to new physics. These beautiful and early achievements also underscore our plans for upgrading the LHC to substantially increase the statistics. The analysis methods have now been shown to reach the precision required for exploration of the full physics landscape, including hopefully new physics that so far hides so subtly,” said CERN Director for Research and Computing Eckhard Elsen.

    Science paper:
    Observation of Higgs boson decay to bottom quarks

    See the full article here.


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  • richardmitnick 3:16 pm on July 18, 2018 Permalink | Reply
    Tags: , , , CERN CMS, , Meenakshi Narain, , , ,   

    From Brown University: Women in STEM- “Brown physicist elected to represent U.S. in Large Hadron Collider experiment” Meenakshi Narain 

    Brown University
    From Brown University

    July 18, 2018
    Kevin Stacey
    kevin_stacey@brown.edu
    401-863-3766

    1
    Meenakshi Narain

    Meenakshi Narain will lead the collaboration board for U.S. institutions participating the CMS experiment at the Large Hadron Collider, an experiment pushing the frontiers of modern particle physics.

    Brown University physics professor Meenakshi Narain has been tapped to chair the collaboration board of U.S. institutions in the Compact Muon Solenoid (CMS) experiment, one of two large-scale experiments happening at the Large Hadron Collider particle accelerator headquartered in Geneva.

    CERN CMS Higgs Event


    CERN/CMS Detector

    The CMS experiment is an international collaboration of 4,000 particle physicists, engineers, computer scientists, technicians and students from approximately 200 institutes and universities around the world. With more than 1,200 participants, the U.S. CMS collaboration is the largest national group in the global experiment. As collaboration board chair, Narain will represent U.S. institutions within the broader collaboration, as well as with U.S. funding agencies. The board also plays a key role in shaping the vision and direction of the U.S. collaboration.

    “I’m honored that my colleagues from the 50 U.S. institutions that collaborate with the CMS Experiment have chosen me to represent them,” Narain said. “I see this position as an opportunity to help U.S. CMS to become a more inclusive community and to enable all young scientists to contribute to their full potential to CMS and find rewarding career opportunities in academia and industry.”

    Narain and other Brown physicists working with the CMS experiment played key roles in the discovery in 2012 of the Higgs Boson, which at the time was the final missing piece in the Standard Model of particle physics. After the Higgs, the CMS experiment has been searching for particles beyond the Standard Model, including a potential candidate particle for dark matter, the mysterious stuff thought to account for a majority of matter in the universe.

    Narain says part of her job is to maintain the research synergy created by the numerous U.S. scientists and institutions involved in the collaboration as they analyze data from the collider’s latest run. At the same time, the experiment must also prepare for the next stage of the Large Hadron Collider program slated to start around 2026. The next stage involves beam intensities five times higher the current level and 10 times more data than has been acquired to date. That will require parts of the CMS detector to be rebuilt.

    “We need the resources to maintain the detector during the current run as well as to start building the upgrades,” Narain said. “I will work with funding agencies to communicate what we’ll need to both maintain our involvement in the data analysis and play a leading role in the upgrade of the detector.”

    Narain says that as the first woman to chair the collaboration board, she plans to work toward cultivating more diversity in what is currently the largest physics collaboration in the U.S.

    “With this comes the opportunity to promote women and other underrepresented minorities to have the opportunity to develop their careers to their fullest potential,” she said. “I hope that I will be able to improve our community in the U.S. and in CMS in general to be more inclusive during my two-year term.”

    Narain joined the Brown faculty in 2007 and has worked at the Large Hadron Collider together with the Brown team that includes professors David Cutts, Ulrich Heintz and Greg Landsberg. She was also a member of the DZero experiment at the Fermi National Accelerator Laboratory, where she played a prominent role in the discoveries of the top quark and the anti-top quark, two fundamental constituents of matter. She is a fellow of the American Physical Society and the author of more than 500 journal articles.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Brown

    Brown U Robinson Hall
    Located in historic Providence, Rhode Island and founded in 1764, Brown University is the seventh-oldest college in the United States. Brown is an independent, coeducational Ivy League institution comprising undergraduate and graduate programs, plus the Alpert Medical School, School of Public Health, School of Engineering, and the School of Professional Studies.

    With its talented and motivated student body and accomplished faculty, Brown is a leading research university that maintains a particular commitment to exceptional undergraduate instruction.

    Brown’s vibrant, diverse community consists of 6,000 undergraduates, 2,000 graduate students, 400 medical school students, more than 5,000 summer, visiting and online students, and nearly 700 faculty members. Brown students come from all 50 states and more than 100 countries.

    Undergraduates pursue bachelor’s degrees in more than 70 concentrations, ranging from Egyptology to cognitive neuroscience. Anything’s possible at Brown—the university’s commitment to undergraduate freedom means students must take responsibility as architects of their courses of study.

     
  • richardmitnick 9:23 am on June 4, 2018 Permalink | Reply
    Tags: , , , CERN CMS, , , , ,   

    From CERN Courier: “Higgs boson reaches the top” 


    From CERN Courier

    Jun 1, 2018
    No writer credit

    The CMS collaboration has published the first direct observation of the coupling between the Higgs boson and the top quark, offering an important probe of the consistency of the Standard Model (SM). In the SM, the Higgs boson interacts with fermions via a Yukawa coupling, the strength of which is proportional to the fermion mass. Since the top quark is the heaviest particle in the SM, its coupling to the Higgs boson is expected to be the largest and thus the dominant contribution to many loop processes, making it a sensitive probe of hypothetical new physics.

    1
    Combined likelihood analysis

    The associated production of a Higgs boson with a top quark–antiquark pair (ttH) is the best direct probe of the top-Higgs Yukawa coupling with minimal model dependence, and thus a crucial element to verify the SM nature of the Higgs boson. However, its small production rate – constituting only about 1% of the total Higgs production cross-section – makes the ttH measurement a considerable challenge.

    The CMS and ATLAS collaborations reported first evidence for the process last year, based on LHC data collected at a centre-of-mass energy of 13 TeV (CERN Courier May 2017 p49 and December 2017 p12). The first observation, constituting statistical significance above five standard deviations, is based on an analysis of the full 2016 CMS dataset recorded at an energy of 13 TeV and by combining these results with those collected at lower energies.

    The ttH process gives rise to a wide variety of final states, and the new CMS analysis combines results from a number of them. Top quarks decay almost exclusively to a bottom quark (b) and a W boson, the latter subsequently decaying either to a quark and an antiquark or to a charged lepton and its associated neutrino. The Higgs-boson decay channels include the decay to a bb quark pair, a τ+τ– lepton pair, a photon pair, and combinations of quarks and leptons from the decay of intermediate on- or off-shell W and Z bosons. These five Higgs-boson decay channels were analysed by CMS using sophisticated methods, such as multivariate techniques, to separate signal from background events. Each channel poses different experimental challenges: the bb channel has the largest rate but suffers from a large background of events containing a top-quark pair and jets, while the photon and Z-boson pair channels offer the highest signal-to-background ratio at a very small rate.

    CMS observed an excess of events with respect to the background-only hypothesis at a significance of 5.2 standard deviations. The measured values of the signal strength in the considered channels are consistent with each other, and a combined value of 1.26 +0.31/–0.26 times the SM expectation is obtained (see figure). The measured production rate is thus consistent with the SM prediction within one standard deviation. The result establishes the direct Yukawa coupling of the Higgs boson to the top quark, marking an important milestone in our understanding of the properties of the Higgs boson.

    Further reading

    https://arxiv.org/abs/1804.02610
    https://arxiv.org/abs/1803.05485
    https://journals.aps.org/prd/abstract/10.1103/PhysRevD.97.072003

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings
    Please help promote STEM in your local schools.


    Stem Education Coalition

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

     
  • richardmitnick 8:58 am on June 4, 2018 Permalink | Reply
    Tags: , , , CERN CMS, , , ,   

    From CERN CMS and ATLAS: “The Higgs boson reveals its affinity for the top quark” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    New results from the ATLAS and CMS experiments at the LHC reveal how strongly the Higgs boson interacts with the heaviest known elementary particle, the top quark, corroborating our understanding of the Higgs and setting constraints on new physics.

    CERN CMS Event NOV 2010

    From CERN CMS

    By CMS

    The first observation of the simultaneous production of a Higgs boson with a top quark-antiquark pair is being published today in the journal Physical Review Letters. This major milestone, first reported by the CMS Collaboration in early April 2018, unambiguously demonstrates the interaction of the Higgs boson and top quarks, which are the heaviest known subatomic particles. It is an important step forward in our understanding of the origin of mass. The paper features as a PRL Editors’ Suggestion and also has a Physics Viewpoint article published about it.

    ________________________________________________________
    From CMS – first reported by the CMS Collaboration in early April 2018

    The observation of a Higgs boson in 2012 at the Large Hadron Collider marked the starting point of a broad experimental program to determine the properties of the newly discovered particle. In the standard model, the Higgs boson couples to fermions in a Yukawa-type interaction, with a coupling strength proportional to the fermion mass. While decays into γγ, ZZ, WW, and ττ final states have been observed and there is evidence for the direct decay of the particle to the bb (down-type quarks) final state, the decay to the tt (up-type quarks) final state is not kinematically possible. Therefore, it is of paramount importance to probe the coupling of the Higgs boson to the top quark, the heaviest known fermion, by producing the Higgs in the fusion of a top quark-antiquark pair (left diagram) or through radiation from a top quark (right diagram).

    1

    The associated production of a Higgs boson and a top quark-antiquark pair (ttH production) is a direct probe of the top–Higgs coupling. Hence the observation of this production mechanism is one of the primary objectives of the the Higgs physics program at the LHC.

    The CMS experiment has searched for ttH production in the data collected at the center-of-mass energies of 7, 8, and 13 TeV with the Higgs boson decaying to pairs of W bosons, Z bosons, photons, τ leptons, or bottom quark jets. The results have been combined to maximize the sensitivity to this challenging and yet fundamental process.

    3
    An excess of events is observed, with a significance of 5.2 standard deviations, over the expectation from the background-only hypothesis. The corresponding expected significance for the standard model Higgs boson with a mass of 125.09 GeV is 4.2 standard deviations. The measured production rate is consistent with the standard model prediction within one standard deviation.

    In addition to comprising the first observation of a new Higgs boson production mechanism, this measurement establishes the tree-level coupling of the Higgs boson to the top quark, and hence to an up-type quark, and is another milestone towards the measurement of the Higgs boson coupling to fermions.
    ________________________________________________________

    4

    An event candidate for the production of a top quark and top anti-quark pair in conjunction with a Higgs Boson in the CMS detector. The Higgs decays into a tau+ lepton and a tau- lepton; the tau+ in turn decays into hadrons and the tau- decays into an electron. The decay product symbols are in blue. The top quark decays into three jets (sprays of lighter particles) whose names are given in purple. One of these is initiated by a b-quark. The top anti-quark decays into a muon and b-jet, whose names appear in red.

    Further reading:

    [1] CMS ttH observation journal article: Physical Review Letters, June 4, 2018

    See the full CMS article here.

    From CERN ATLAS

    6
    CERN ATLAS Event 2012

    New ATLAS result establishes production of Higgs boson in association with top quarks.

    This rare process is one of the most sensitive tests of the Higgs mechanism.

    By ATLAS Collaboration, 4th June 2018

    According to the Standard Model, quarks, charged leptons, and W and Z bosons obtain their mass through interactions with the Higgs field, a quantum fluctuation of which gives rise to the Higgs boson. To test this theory, ATLAS takes high-precision measurements of the interactions between the Higgs boson and these particles. While the ATLAS and CMS experiments at CERN’s Large Hadron Collider (LHC) had observed and measured the Higgs boson decaying to pairs of W or Z bosons, photons or tau leptons, the Higgs coupling to quarks had not – despite evidence – been observed.

    In results presented today at the LHCP2018 conference, the ATLAS Collaboration has observed the production of the Higgs boson together with a top-quark pair (known as “ttH” production). Only about 1% of all Higgs bosons are produced through this rare process. This result establishes a direct measurement of the interaction between the top quark and the Higgs boson (known as the “top quark Yukawa coupling”). As the top quark is the heaviest particle in the Standard Model, this measurement is one of the most sensitive tests of the Higgs mechanism.

    Previous ATLAS measurements using 2015 and 2016 data provided the first evidence for ttH production from a combination of channels where the Higgs boson decayed to two W or Z bosons (WW* or ZZ*), to a pair of tau leptons, to a pair of b-quarks, or to a pair of photons (“diphoton”). Those results have now been updated with the measurements of the diphoton and ZZ* decay modes that use the larger 2015-2017 dataset, and where improved reconstruction algorithms and new analysis techniques have increased the sensitivity of the measurements. The CMS Collaboration recently reported the observation of ttH production by combining 2015 and 2016 data with data taken at lower collision energies in earlier LHC runs.
    Evidence for ttH production in the diphoton channel in the 2015-2017 dataset

    The probability of a Higgs boson decaying to a diphoton pair is only about 0.2%, making the predicted rate for ttH production in this channel quite small. However, because the energy and direction of photons can be well measured with the ATLAS detector, the reconstructed mass peak obtained with this decay mode is narrow. It is therefore possible to observe a signal even when the number of events is low. Furthermore, regions with lower and higher reconstructed mass (called the “sidebands”) can be used to estimate the background under the signal peak using the data themselves, rendering this channel particularly robust.

    To optimize the measurement ATLAS employs machine learning techniques. Events consistent with the ttH kinematics are selected using “boosted decision tree” (BDT) algorithms that allow physicists to separate the events into multiple categories with different signal-to-background abundance ratios. Depending on the top-quark decay channel considered, the inputs given to the BDT are the momenta of the “jets” (collimated groups of particles that are produced by a quark or gluon), leptons and photons observed in each event. As the decay of a top quark always produces a b-quark, identifying jets that arise from b-quarks is essential for reducing backgrounds. To achieve this, ATLAS developed a b-identification algorithm (also based on machine learning); the b-identification decision for each jet is included in the BDT inputs.

    4
    Figure 1: Time-lapse animation showing the increasing ttH signal in the diphoton mass spectrum as more data are included in the measurement. (Image: ATLAS Collaboration/CERN)

    Each category is analysed separately by studying the distribution of the invariant mass of the diphoton candidates in selected events. This distribution is fit to a combination of signal (Higgs boson decay to diphoton in events containing a top-quark pair) and background (cases where the diphoton candidate does not arise from a Higgs boson or where the event does not contain a true top-quark pair). The numbers of fitted signal events in the different categories are then statistically combined, taking into account correlated experimental and theoretical systematic uncertainties.

    The result of the above procedure, using 80 fb-1 of data recorded in 2015, 2016 and the recent 2017 run of the LHC, is summarised in Figure 1, which shows the diphoton invariant mass distribution, summed over categories weighted by their signal purity. The significance of the observed signal is 4.1 standard deviations; the expected significance for Standard Model production is 3.7 standard deviations.

    Search continues for ttH production in the ZZ* channel in the 2015-2017 dataset.

    The decay of a Higgs boson to ZZ* with the subsequent decay of the ZZ* to four leptons is another channel where the Higgs mass peak is narrow. Due to the very clean detector signature of the four-lepton decay mode, this channel is essentially free of backgrounds apart from small contributions from Higgs bosons produced through other production modes than ttH. However, this decay mode is even rarer than that of diphotons, with less than one event expected from ttH production in the 80 fb-1 of the full 2015-2017 dataset. A dedicated search for this decay was performed, but no candidate events were found in the 2015-2017 ATLAS data.

    5
    Figure 2: Combined ttH production cross section, as well as cross sections measured in the individual analyses, divided by the SM cross section prediction. ML indicates the analysis of the two and three lepton final states (multilepton). The black lines show the total uncertainties, while the bands indicate the statistical and systematic uncertainties. The red line indicates the SM cross section prediction, and the grey band represents the theoretical uncertainties on the prediction. For the γγ and ZZ* channels to full dataset at 13 GeV (collected between 2015 and 2017) have been used, whereas the results of the other channels are based on the 2015 and 2016 data. (Image: ATLAS Collaboration/CERN)

    Combination with earlier ATLAS results

    The measurements described above have been combined with the previously reported searches for ttH that used 2015 and 2016 data. Decays of the Higgs boson to a b-quark pair and to a pair of W bosons or tau leptons had observed (expected) significances of 1.4 (1.6) and 4.2 (2.8) standard deviations, respectively.

    After the combination, the observed (expected) significance of the signal over the background is 5.8 (4.9) standard deviations. The ratio of the combined ttH cross section measurement and the cross section measurements separated by Higgs boson decay modes are presented in Figure 2. The measured ratio of 1.32 ± 0.27 is slightly larger than, but consistent with the Standard Model expectation.

    Further searches for the ttH process were performed using 7 and 8 TeV data collected during Run 1. When combined with the 2015-2017 results, the observed (expected) significance is 6.3 (5.1) standard deviations.

    Summary

    ATLAS has observed the production of the Higgs boson in association with a top-quark pair with a significance of 6.3 standard deviations over the background-only hypothesis. The measured ttH production cross section is consistent with the Standard Model prediction. This measurement provides direct evidence for the coupling of the Higgs boson to the top quark and supports the Standard Model mechanism whereby the top quark obtains its mass through interaction with the Higgs field.

    Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector Physical Review D

    See the full ATLAS article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.
    stem
    Stem Education Coalition

    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

    OTHER PROJECTS AT CERN

    CERN AEGIS

    CERN ALPHA

    CERN ALPHA

    CERN AMS

    CERN ACACUSA

    CERN ASACUSA

    CERN ATRAP

    CERN ATRAP

    CERN AWAKE

    CERN AWAKE

    CERN CAST

    CERN CAST Axion Solar Telescope

    CERN CLOUD

    CERN CLOUD

    CERN COMPASS

    CERN COMPASS

    CERN DIRAC

    CERN DIRAC

    CERN ISOLDE

    CERN ISOLDE

    CERN LHCf

    CERN LHCf

    CERN NA62

    CERN NA62

    CERN NTOF

    CERN TOTEM

    CERN UA9

     
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