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  • richardmitnick 3:36 pm on September 22, 2017 Permalink | Reply
    Tags: , ATLAS hunts for new physics with dibosons, CERN ATLAS, , , ,   

    From CERN Courier: “ATLAS hunts for new physics with dibosons” 


    CERN Courier

    Sep 22, 2017

    1
    WZ data

    Beyond the Standard Model of particle physics (SM), crucial open questions remain such as the nature of dark matter, the overabundance of matter compared to antimatter in the universe, and also the mass scale of the scalar sector (what makes the Higgs boson so light?). Theorists have extended the SM with new symmetries or forces that address these questions, and many such extensions predict new resonances that can decay into a pair of bosons (diboson), for example: VV, Vh, Vγ and γγ, where V stands for a weak boson (W and Z), h for the Higgs boson, and γ is a photon.

    The ATLAS collaboration has a broad search programme for diboson resonances, and the most recent results using 36 fb–1 of proton–proton collision data at the LHC taken at a centre-of-mass energy of 13 TeV in 2015 and 2016 have now been released. Six different final states characterised by different boson decay modes were considered in searches for a VV resonance: 4ℓ, ℓℓνν, ℓℓqq, ℓνqq, ννqq and qqqq, where ℓ, ν and q stand for charged leptons (electrons and muons), neutrinos and quarks, respectively. For the Vh resonance search, the dominant Higgs boson decay into a pair of b-quarks (branching fraction of 58%) was exploited together with four different V decays leading to ℓℓbb, ℓνbb, ννbb and qqbb final states. A Zγ resonance was sought in final states with two leptons and a photon.

    A new resonance would appear as an excess (bump) over the smoothly distributed SM background in the invariant mass distribution reconstructed from the final-state particles. The left figure shows the observed WZ mass distribution in the qqqq channel together with simulations of some example signals. An important key to probe very high-mass signals is to identify high-momentum hadronically decaying V and h bosons. ATLAS developed a new technique to reconstruct the invariant mass of such bosons combining information from the calorimeters and the central tracking detectors. The resulting improved mass resolution for reconstructed V and h bosons increased the sensitivity to very heavy signals.

    No evidence for a new resonance was observed in these searches, allowing ATLAS to set stringent exclusion limits. For example, a graviton signal predicted in a model with extra spatial dimensions was excluded up to masses of 4 TeV, while heavy weak-boson-like resonances (as predicted in composite Higgs boson models) decaying to WZ bosons are excluded for masses up to 3.3 TeV. Heavier Higgs partners can be excluded up to masses of about 350 GeV, assuming specific model parameters.

    See the full article here .

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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

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  • richardmitnick 6:15 pm on September 18, 2017 Permalink | Reply
    Tags: , , , , CERN ATLAS, , , , ,   

    From BNL: “Three Brookhaven Lab Scientists Selected to Receive Early Career Research Program Funding” 

    Brookhaven Lab

    August 15, 2017 [Just caught up with this via social media.]
    Karen McNulty Walsh,
    kmcnulty@bnl.gov
    (631) 344-8350
    Peter Genzer,
    genzer@bnl.gov
    (631) 344-3174

    Three scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have been selected by DOE’s Office of Science to receive significant research funding through its Early Career Research Program.

    The program, now in its eighth year, is designed to bolster the nation’s scientific workforce by providing support to exceptional researchers during the crucial early career years, when many scientists do their most formative work. The three Brookhaven Lab recipients are among a total of 59 recipients selected this year after a competitive review of about 700 proposals.

    The scientists are each expected to receive grants of up to $2.5 million over five years to cover their salary plus research expenses. A list of the 59 awardees, their institutions, and titles of research projects is available on the Early Career Research Program webpage.

    This year’s Brookhaven Lab awardees include:

    1
    Sanjaya Senanayake

    Brookhaven Lab chemist Sanjaya D. Senanayake was selected by DOE’s Office of Basic Energy Sciences to receive funding for “Unraveling Catalytic Pathways for

    Low Temperature Oxidative Methanol Synthesis from Methane.” His overarching goal is to study and improve catalysts that enable the conversion of methane (CH4), the primary component of natural gas, directly into methanol (CH3OH), a valuable chemical intermediate and potential renewable fuel.

    This research builds on the recent discovery of a single step catalytic process for this reaction that proceeds at low temperatures and pressures using inexpensive earth abundant catalysts. The reaction promises to be more efficient than current multi-step processes, which are energy-intensive, and a significant improvement over other attempts at one-step reactions where higher temperatures convert most of the useful hydrocarbon building blocks into carbon monoxide and carbon dioxide rather than methanol. With Early Career funding, Senanayake’s team will explore the nature of the reaction, and build on ways to further improve catalytic performance and specificity.

    The project will exploit unique capabilities of facilities at Brookhaven Lab, particularly at the National Synchrotron Light Source II (NSLS-II), that make it possible to study catalysts in real-world reaction environments (in situ) using x-ray spectroscopy, electron imaging, and other in situ methods.

    BNL NSLS-II


    BNL NSLS II

    Experiments using well defined model surfaces and powders will reveal atomic level catalytic structures and reaction dynamics. When combined with theoretical modeling, these studies will help the scientists identify the essential interactions that take place on the surface of the catalyst. Of particular interest are the key features that activate stable methane molecules through “soft” oxidative activation of C-H bonds so methane can be converted to methanol using oxygen (O2) and water (H2O) as co-reactants.

    This work will establish and experimentally validate principles that can be used to design improved catalysts for synthesizing fuel and other industrially relevant chemicals from abundant natural gas.

    “I am grateful for this funding and the opportunity to pursue this promising research,” Senanayake said. “These fundamental studies are an essential step toward overcoming key challenges for the complex conversion of methane into valued chemicals, and for transforming the current model catalysts into practical versions that are inexpensive, durable, selective, and efficient for commercial applications.”

    Sanjaya Senanayake earned his undergraduate degree in material science and Ph.D. in chemistry from the University of Auckland in New Zealand in 2001 and 2006, respectively. He worked as a research associate at Oak Ridge National Laboratory from 2005-2008, and served as a local scientific contact at beamline U12a at the National Synchrotron Light Source (NSLS) at Brookhaven Lab from 2005 to 2009. He joined the Brookhaven staff as a research associate in 2008, was promoted to assistant chemist and associate chemist in 2014, while serving as the spokesperson for NSLS Beamline X7B. He has co-authored over 100 peer reviewed publications in the fields of surface science and catalysis, and has expertise in the synthesis, characterization, reactivity of catalysts and reactions essential for energy conversion. He is an active member of the American Chemical Society, North American Catalysis Society, the American Association for the Advancement of Science, and the New York Academy of Science.

    3
    Alessandro Tricoli

    Brookhaven Lab physicist Alessandro Tricoli will receive Early Career Award funding from DOE’s Office of High Energy Physics for a project titled “Unveiling the Electroweak Symmetry Breaking Mechanism at ATLAS and at Future Experiments with Novel Silicon Detectors.”

    CERN/ATLAS detector

    His work aims to improve, through precision measurements, the search for exciting new physics beyond what is currently described by the Standard Model [SM], the reigning theory of particle physics.

    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.

    The discovery of the Higgs boson at the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) in Switzerland confirmed how the quantum field associated with this particle generates the masses of other fundamental particles, providing key insights into electroweak symmetry breaking—the mass-generating “Higgs mechanism.”

    CERN ATLAS Higgs Event

    But at the same time, despite direct searches for “new physics” signals that cannot be explained by the SM, scientists have yet to observe any evidence for such phenomena at the LHC—even though they know the SM is incomplete (for example it does not include an explanation for gravity).

    Tricoli’s research aims to make precision measurements to test fundamental predictions of the SM to identify anomalies that may lead to such discoveries. He focuses on the analysis of data from the LHC’s ATLAS experiment to comprehensively study electroweak interactions between the Higgs and particles called W and Z bosons. Any discovery of anomalies in such interactions could signal new physics at very high energies, not directly accessible by the LHC.

    This method of probing physics beyond the SM will become even more stringent once the high-luminosity upgrade of ATLAS, currently underway, is completed for longer-term LHC operations planned to begin in 2026.

    Tricoli’s work will play an important role in the upgrade of ATLAS’s silicon detectors, using novel state-of-the art technology capable of precision particle tracking and timing so that the detector will be better able to identify primary particle interactions and tease out signals from the background events. Designing these next-generation detector components could also have a profound impact on the development of future instruments that can operate in high radiation environments, such as in future colliders or in space.

    “This award will help me build a strong team around a research program I feel passionate about at ATLAS and the LHC, and for future experiments,” Tricoli said.

    “I am delighted and humbled by the challenge given to me with this award to take a step forward in science.”

    Alessandro Tricoli received his undergraduate degree in physics from the University of Bologna, Italy, in 2001, and his Ph.D. in particle physics from Oxford University in 2007. He worked as a research associate at Rutherford Appleton Laboratory in the UK from 2006 to 2009, and as a research fellow and then staff member at CERN from 2009 to 2015, receiving commendations on his excellent performance from both institutions. He joined Brookhaven Lab as an assistant physicist in 2016. A co-author on multiple publications, he has expertise in silicon tracker and detector design and development, as well as the analysis of physics and detector performance data at high-energy physics experiments. He has extensive experience tutoring and mentoring students, as well as coordinating large groups of physicists involved in research at ATLAS.

    4
    Chao Zhang

    Brookhaven Lab physicist Chao Zhang was selected by DOE’s Office of High Energy Physics to receive funding for a project titled, “Optimization of Liquid Argon TPCs for Nucleon Decay and Neutrino Physics.” Liquid Argon TPCs (for Time Projection Chambers) form the heart of many large-scale particle detectors designed to explore fundamental mysteries in particle physics.

    Among the most compelling is the question of why there’s a predominance of matter over antimatter in our universe. Though scientists believe matter and antimatter were created in equal amounts during the Big Bang, equal amounts would have annihilated one another, leaving only light. The fact that we now have a universe made almost entirely of matter means something must have tipped the balance.

    A US-hosted international experiment scheduled to start collecting data in the mid-2020s, called the Deep Underground Neutrino Experiment (DUNE), aims to explore this mystery through the search for two rare but necessary conditions for the imbalance: 1) evidence that some processes produce an excess of matter over antimatter, and 2) a sizeable difference in the way matter and antimatter behave.

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


    FNAL DUNE Argon tank at SURF


    Surf-Dune/LBNF Caverns at Sanford



    SURF building in Lead SD USA

    The DUNE experiment will look for signs of these conditions by studying how protons (one of the two “nucleons” that make up atomic nuclei) decay as well as how elusive particles called neutrinos oscillate, or switch identities, among three known types.

    The DUNE experiment will make use of four massive 10-kiloton detector modules, each with a Liquid Argon Time Projection Chamber (LArTPC) at its core. Chao’s aim is to optimize the performance of the LArTPCs to fully realize their potential to track and identify particles in three dimensions, with a particular focus on making them sensitive to the rare proton decays. His team at Brookhaven Lab will establish a hardware calibration system to ensure their ability to extract subtle signals using specially designed cold electronics that will sit within the detector. They will also develop software to reconstruct the three-dimensional details of complex events, and analyze data collected at a prototype experiment (ProtoDUNE, located at Europe’s CERN laboratory) to verify that these methods are working before incorporating any needed adjustments into the design of the detectors for DUNE.

    “I am honored and thrilled to receive this distinguished award,” said Chao. “With this support, my colleagues and I will be able to develop many new techniques to enhance the performance of LArTPCs, and we are excited to be involved in the search for answers to one of the most intriguing mysteries in science, the matter-antimatter asymmetry in the universe.”

    Chao Zhang received his B.S. in physics from the University of Science and Technology of China in 2002 and his Ph.D. in physics from the California Institute of Technology in 2010, continuing as a postdoctoral scholar there until joining Brookhaven Lab as a research associate in 2011. He was promoted to physics associate III in 2015. He has actively worked on many high-energy neutrino physics experiments, including DUNE, MicroBooNE, Daya Bay, PROSPECT, JUNO, and KamLAND, co-authoring more than 40 peer reviewed publications with a total of over 5000 citations. He has expertise in the field of neutrino oscillations, reactor neutrinos, nucleon decays, liquid scintillator and water-based liquid scintillator detectors, and liquid argon time projection chambers. He is an active member of the American Physical Society.

    See the full article here .

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    BNL Campus

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
    i1

     
  • richardmitnick 11:32 am on August 14, 2017 Permalink | Reply
    Tags: , ATLAS sees first direct evidence of light-by-light scattering at high energy, , CERN ATLAS, , ,   

    From ATLAS at CERN: “ATLAS sees first direct evidence of light-by-light scattering at high energy” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    14th August 2017
    Katarina Anthony

    1
    A light-by-light scattering candidate event measured in the ATLAS detector. (Image: ATLAS Collaboration/CERN).

    Physicists from the ATLAS experiment at CERN have found the first direct evidence of high energy light-by-light scattering, a very rare process in which two photons – particles of light – interact and change direction. The result, published today in Nature Physics , confirms one of the oldest predictions of quantum electrodynamics (QED).

    “This is a milestone result: the first direct evidence of light interacting with itself at high energy,” says Dan Tovey (University of Sheffield), ATLAS Physics Coordinator. “This phenomenon is impossible in classical theories of electromagnetism; hence this result provides a sensitive test of our understanding of QED, the quantum theory of electromagnetism.”

    Direct evidence for light-by-light scattering at high energy had proven elusive for decades – until the Large Hadron Collider’s second run began in 2015. As the accelerator collided lead ions at unprecedented collision rates, obtaining evidence for light-by-light scattering became a real possibility. “This measurement has been of great interest to the heavy-ion and high-energy physics communities for several years, as calculations from several groups showed that we might achieve a significant signal by studying lead-ion collisions in Run 2,” says Peter Steinberg (Brookhaven National Laboratory), ATLAS Heavy Ion Physics Group Convener.

    Heavy-ion collisions provide a uniquely clean environment to study light-by-light scattering. As bunches of lead ions are accelerated, an enormous flux of surrounding photons is generated. When ions meet at the centre of the ATLAS detector, very few collide, yet their surrounding photons can interact and scatter off one another. These interactions are known as ‘ultra-peripheral collisions’.

    Studying more than 4 billion events taken in 2015, the ATLAS collaboration found 13 candidates for light-by-light scattering. This result has a significance of 4.4 standard deviations, allowing the ATLAS collaboration to report the first direct evidence of this phenomenon at high energy.

    “Finding evidence of this rare signature required the development of a sensitive new ‘trigger’ for the ATLAS detector,” says Steinberg. “The resulting signature — two photons in an otherwise empty detector — is almost the diametric opposite of the tremendously complicated events typically expected from lead nuclei collisions. The new trigger’s success in selecting these events demonstrates the power and flexibility of the system, as well as the skill and expertise of the analysis and trigger groups who designed and developed it.”

    ATLAS physicists will continue to study light-by-light scattering during the upcoming LHC heavy-ion run, scheduled for 2018. More data will further improve the precision of the result and may open a new window to studies of new physics. In addition, the study of ultra-peripheral collisions should play a greater role in the LHC heavy-ion programme, as collision rates further increase in Run 3 and beyond.

    See the full article here .

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  • richardmitnick 8:25 am on August 3, 2017 Permalink | Reply
    Tags: 5 fundamental parameters from top quark decay, , CERN ATLAS, , ,   

    From ATLAS: “5 fundamental parameters from top quark decay” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    3rd August 2017
    ATLAS Collaboration

    Number 4 may shock you!

    1
    Figure 1: The radiation of decay products from a polarized top quark follows patterns like those shown here. An analysis of the radiation is used to measure top quark properties in a new analysis. (Image: ATLAS Collaboration/CERN)

    For many physicists, discovering “new physics” means bringing to light a new particle. Another path to discovery lies in carefully measuring the properties of known particles and the interactions between them. The ATLAS experiment has now released new results on the top quark’s interaction with the charged intermediate vector boson.

    While the Higgs boson, which escaped observation until as recently as 2012, is certainly the most intriguing elementary particle, the top quark is arguably second. Heavier than even the Higgs boson, the top quark packs as much mass as a gold nucleus into a single point like constituent. Precise measurements of the top quark have taken a great leap forward at the Large Hadron Collider (LHC), where the production rate is high and the backgrounds are low.

    In the recent paper [JHEP], the ATLAS collaboration presents results obtained from decays of polarized top quarks. The polarization occurs when top quarks are produced singly through the parity-violating weak interaction, rather than in pairs through the parity-conserving strong interaction. Singly-produced top quarks have only recently become an important tool for discovery.

    2
    Figure 2: The plot shows the strength of each of the decay patterns such as those shown in Figure 1. The red solid line is the Standard Model expectation. The data points are the measurement. The measurement is in very good agreement with the Standard Model. (Image: ATLAS Collaboration/CERN)

    Nine distinct decay patterns, examples of which are shown in Figure 1, can be discerned in these decays, similar to antennae patterns. These patterns depend upon five fundamental constants (called f1, f1+,f0+,δ-, and P) governing the interaction between the top, its partner the bottom quark, and the charged weak boson (W±). Current understanding of physics holds that the top quark couplings should be “left-handed” like those of the other quarks, and that they should be identical between the top quarks and its antiparticle, the top antiquark. The new measurements put that understanding to the test.

    By studying the full multidimensional decay patterns, ATLAS measures many properties of the top-bottom-W interaction at the same time and without some of the assumptions that have been made in the past. The analysis is known for both its complexity and its power. Results are shown in Figure 2. Five fundamental constants are determined from the decay. The fourth one, δ–, quantifies the matter-antimatter asymmetry in top quark decays. It is consistent with zero and consistent with the current understanding of fundamental physics. Shocking? Maybe – but physicists are slowly getting used to the idea that the Standard Model is an excellent description of nature.

    The analysis uses proton–antiproton collisions at 8 TeV, data collected at the LHC in 2012. Investigators are now applying even more refined techniques to collisions at a higher centre-of-mass energy of 13 TeV now being collected at CERN. Future measurements at higher precision may finally observe deviations from the Standard Model.

    Links:

    Analysis of the Wtb vertex from the measurement of triple-differential angular decay rates of single top quarks produced in the t-channel at s√ = 8 TeV with the ATLAS detector (arXiv:1707.05393) [Above].
    EPS 2017 presentation by Susana Cabrera Urban: Anomalous couplings in single top and searches for rare top quark couplings with the ATLAS detector
    See also the full lists of ATLAS Conference Notes and ATLAS Physics Papers.

    See the full article here .

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  • richardmitnick 12:01 pm on July 9, 2017 Permalink | Reply
    Tags: , , CERN ATLAS, , , , Probing physics beyond the Standard Model with heavy vector bosons   

    From ATLAS: “Probing physics beyond the Standard Model with heavy vector bosons” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    8th July 2017
    ATLAS Collaboration

    1
    Figure 1: The reconstructed mass of the selected candidate events decaying to WW or ZZ bosons, with the qqqq final state. The black markers represent the data. The blue and green curves represent the hypothesized signal for two different masses. The red curve represents the Standard Model processes. (Image: ATLAS Collaboration/CERN)

    Although the discovery of the Higgs boson by the ATLAS and CMS Collaborations in 2012 completed the Standard Model, many mysteries remain unexplained. For instance, why is the mass of the Higgs boson so much lighter than one would expect and why is gravity so weak?

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    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.

    Numerous models beyond the Standard Model attempt to explain these mysteries. Some explain the apparent weakness of gravity by introducing additional dimensions of space in which gravity propagates. One model goes beyond that, and considers the real world as a higher-dimensional universe described by warped geometry, which leads to strongly interacting massive graviton states. Other models propose, for example, additional types of Higgs bosons.

    All these models predict the existence of new heavy particles that can decay into pairs of massive weak bosons (WW, WZ or ZZ). The search for such particles has benefited greatly from the increase in the proton–proton collision energy during Run 2 of the Large Hadron Collider (LHC).

    _______________________________________________________________________
    The search for new heavy particles has benefited greatly from the LHC’s increase in proton–proton collision energy.
    _______________________________________________________________________

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    Figure 2: The limit on the cross-section times branching ratio of hypothetical particle described by one of the models for the different final states. (Image: ATLAS Collaboration/CERN)

    The W and Z bosons are carrier particles that mediate the weak force. They decay into other Standard Model particles, like charged leptons (l), neutrinos (ν) and quarks (q). These particles are reconstructed differently in the detector. Quarks, for instance, are reconstructed as localized sprays of hadrons, denoted jets. The two bosons could yield several combinations of these particles in the final states. The ATLAS Collaboration has released results on searches involving all relevant decays of the boson pair: ννqq, llqq, lνqq and qqqq (where the lepton is an electron or muon).

    What do these searches have in common? In each of these, at least one of the bosons decays into a pair of quarks. When the sought-after particle is very massive, the two bosons from its decay are ejected with such large momenta that their respective decay products are collimated and the pair of quarks merge into a single large jet. This phenomenon provides a powerful means to distinguish the new physics signal from strong-interaction Standard Model processes. As some exemplary results of the searches, Figure 1 shows the distributions of the reconstructed mass of the candidate particle. Figure 2 shows the limit on the cross-section times branching ratio of a hypothetical particle described by one of the models.

    So far, no evidence of a new particle has been observed. The search continues with increased sensitivity as ATLAS collects more data.

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

    See the full article here .

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  • richardmitnick 7:00 am on July 7, 2017 Permalink | Reply
    Tags: , CERN ATLAS, , , ,   

    From ATLAS: “Why should there be only one? Searching for additional Higgs Bosons beyond the Standard Model” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    6th July 2017
    ATLAS Collaboration

    1
    Figure 1: Feynman diagram for leading order production of a neutral MSSM Higgs boson in association with b-quarks. (Image: ATLAS Collaboration/CERN)

    CERN CMS Higgs Event

    Since the discovery of the elusive Higgs boson in 2012, researchers have been looking beyond the Standard Model to answer many outstanding questions. An attractive extension to the Standard Model is Supersymmetry (SUSY), which introduces a plethora of new particles, some of which may be candidates for Dark Matter.

    Standard model of Supersymmetry DESY

    One of the most popular SUSY models – the Minimal Supersymmetric Standard Model (MSSM) – predicts the existence of five Higgs bosons. In this model, the recently discovered Higgs boson (h) would be considered to be the lightest of the set. Two charged Higgs (H+, H–) and two neutral Higgs (A/H) would complete the set, and could exist within a wide range of masses above that of the discovered Higgs boson. The LHC experiments are poised to search for these additional bosons using techniques similar to those used in the initial Higgs searches.

    In July 2017, the ATLAS collaboration presented a new result on the search for neutral (A/H) Higgs bosons decaying to two tau leptons. Taus are particularly interesting to the search as there is a stronger coupling between A/H and down-type fermions (e, μ, τ, d, s, b) for certain values of the MSSM parameter-space. This will enhance the probability of decays to tau leptons, as well as the production of A/H in association with b-quarks (Figure 1), providing a larger cross-section. Like with the Standard Model Higgs boson, gluon-fusion production of A/H remains an important production process in the MSSM to varying degrees (depending on the chosen model parameters). Thus, by classifying events by their probability of containing b-flavoured jets, the ATLAS search has been optimised for both b-associated and gluon-fusion production of A/H, respectively.

    2
    Figure 2 (left): The observed and expected 95% CL upper limits on the production cross section times di-tau branching fraction for a scalar boson produced via b-associated production. Figure 3 (right): The observed and expected 95% CL limits on tanβ as a function of the mass of the A boson in the hMSSM scenario. The area above the black curve has been excluded. The exclusion arising from the Standard Model Higgs boson coupling measurements and the exclusion limit from the ATLAS 2015 H/A→ ττ search are shown. (Images: ATLAS Collaboration/CERN)

    See the full article here .

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  • richardmitnick 1:18 pm on July 6, 2017 Permalink | Reply
    Tags: , , CERN ATLAS, Chasing the invisible, , , ,   

    From ATLAS: “Chasing the invisible” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    6th July 2017
    ATLAS Collaboration

    1
    Figure 1: The second highest ETmiss monojet event in the 2016 ATLAS data. A jet with pT of 1707 GeV is indicated by the green and yellow bars corresponding to the energy deposition in the electromagnetic and hadronic calorimeters respectively. The ETmiss of 1735 GeV is shown as the white dashed line in the opposite side of the detector. No additional jets with pT above 30 GeV are found. (Image: ATLAS Collaboration/CERN)

    Cosmological and astrophysical observations based on gravitational interactions indicate that the matter described by the Standard Model of particle physics constitutes only a small fraction of the entire known Universe. These observations infer the existence of Dark Matter, which, if of particle nature, would have to be beyond the Standard Model.

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

    Although the existence of Dark Matter is well-established, its nature and properties still remain one of the greatest unsolved puzzles of fundamental physics. Excellent candidates for Dark Matter particles are weakly interacting massive particles (WIMPs). These “invisible” particles cannot be detected directly by collision experiments.

    At the LHC, most collisions of protons produce sprays of energetic particles that bundle together into so-called “jets”. Momentum conservation requires that if particles are reconstructed in one part of the detector there have to be recoiling particles in the opposite direction. However, if WIMPs are produced they will leave no trace in the detector, causing a momentum imbalance called “missing transverse momentum” (ETmiss). However, a pair of WIMPs can be produced together with a quark or gluon that is radiated from an incoming parton (a generic constituent of the proton) producing a jet which allows to tag this kind of events.

    The jets+ETmiss search looks at final states where a highly energetic jet is produced in association with large ETmiss. Many beyond the Standard Model theories can be probed by looking for an excess of events with large missing transverse momentum compared to the Standard Model expectation. Among those theories, Supersymmetry and models which foresee the existence of Large Extra Spatial Dimensions (LED), predict additional particles that are invisible to collider experiments. These theories could give an elegant explanation to several anomalies still unsolved in the Standard Model.

    2
    Figure 2: Missing transverse momentum distribution after the jets+ETmiss selection in data and in the Standard Model predictions. The different background processes are shown in different colors. The expected spectra of LED, Supersymmetric and WIMP scenarios are also illustrated with dashed lines. (Image: ATLAS Collaboration/CERN)

    The combination of data-driven techniques and high-precision theoretical calculations has allowed ATLAS to predict the main Standard Model background processes with great precision. The shape of the ETmiss spectrum is used to increase the discovery potential of the analysis and increase the discrimination power between signals and background.

    The figure shows the missing transverse momentum spectrum compared to the measurement with the Standard Model expectation. Since no significant excess is observed, the level of agreement between data and the prediction is translated into limits on unknown parameters of the Dark Matter, Supersymmetry and LED models.

    In the WIMP scenario, the latest analysis using data collected in 2015 and 2016 in a specific interaction model are able to exclude Dark Matter masses up to 440 GeV and interaction mediators up to 1.55 TeV. Under the considered model, these represent competitive results when compared with other experiments using different detection approaches.

    Over the next two years the LHC aims to increase the data available by a factor of three. This will be a unique opportunity for ATLAS to investigate the energy frontier and the jets+ETmiss channel will continue to hold the potential to profoundly revise our understanding of the universe.

    Links:

    Search for dark matter and other new phenomena in events with an energetic jet and large missing transverse momentum using the ATLAS detector (ATLAS-CONF-2017-060): link coming soon
    EPS 2017 presentation by Shin-Shan Yu: Dark matter searches at colliders
    See also the full lists of ATLAS Conference Notes and ATLAS Physics Papers.

    See the full article here .

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  • richardmitnick 12:10 pm on July 6, 2017 Permalink | Reply
    Tags: , ATLAS takes a closer look at the Higgs boson’s couplings to other bosons, CERN ATLAS, , ,   

    From ATLAS: “ATLAS takes a closer look at the Higgs boson’s couplings to other bosons” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    6th July 2017
    ATLAS Collaboration

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    Figures 1 and 2: Measurement of the Higgs boson production cross sections in its main production modes and normalised to the Standard Model predictions, as obtained by the H→ZZ*→4ℓ and H→γγ decay channels respectively. (Image: ATLAS Collaboration/CERN)

    Since resuming operation for Run 2, the LHC has been producing about 20,000 Higgs bosons per day in its 13 TeV proton–proton collisions. At the end of 2015, the data collected by the ATLAS and CMS collaborations were already enough to re-observe the Higgs boson at the new collision energy. Now, having recorded more than 36,000 trillion collisions between 2015 and 2016, ATLAS can perform ever more precise measurements of the properties of the Higgs boson.

    Measuring how the Higgs boson is produced and it decays is one of the major goals of the LHC experiments. Greater precision in these measurements allows us to refine our understanding of the Higgs sector of the Standard Model, and also constrain new phenomena beyond the Standard Model that would modify the coupling of the Higgs with the other Standard Model particles. By studying the Higgs boson decays to photon pairs (H→γγ) and to four leptons via intermediate Z bosons (H→ZZ*→4ℓ, where the ‘*’ indicates that one Z boson is produced off its mass shell), the ATLAS experiment can measure the coupling properties of the Higgs boson with unprecedented precision.

    At the LHC, the Higgs boson is produced through different processes with very different rates: gluon fusion, vector-boson fusion, WH, ZH, and ttH. To probe these production modes, ATLAS has introduced a set of criteria to categorize the Higgs events with the H→γγ and H→ZZ*→4ℓ final states. The results of this study are displayed in Figures 1 and 2, where the measured cross section, normalized to the value predicted by the Standard Model, is shown.

    ___________________________________________________________________________________

    Combining these separate measurements allowed ATLAS to bring the experimental sensitivity closer to the precision of the Standard Model predictions.
    ___________________________________________________________________________________

    With the LHC producing an ever-increasing number of Higgs bosons, ATLAS has been able to start measuring the cross section of each production mode in different phase-spaces, setting an additional stress test for the Standard Model. These results are used to constrain possible modifications of the Higgs boson couplings from those predicted by the Standard Model. No significant deviation from the prediction has yet been observed.

    The H→γγ decay channel is also used to measure several differential cross sections for observables sensitive to Higgs boson production and decay, where good agreement was found between the data and Standard Model predictions (see Figure 4). Similar measurements have already been performed with H→ZZ∗→4ℓ decays.

    Combining these separate measurements allowed ATLAS to bring the experimental sensitivity closer to the precision of the Standard Model predictions. The total Higgs boson production cross section is measured to be 57.0 +6.0−5.9 +3.2−2.7 pb, where the first uncertainty is statistical and the second of systematic origin. The result is consistent with the Standard Model prediction of 55.6+2.4−3.4 pb. (Figure 3)

    ATLAS will continue to study the Higgs boson properties for the rest of Run 2, isolating its rare production modes and measuring its more elusive properties. Uncovering these secrets will either further cement the Standard Model, or give us insight of what lies beyond.

    3
    Figure 3: Total Higgs boson production cross sections measured at centre-of-mass energies of 7, 8, and 13 TeV by the H→γγ and H→ZZ*→4ℓ* channels and their combinations, compared to the Standard Model predictions. (Image: ATLAS Collaboration/CERN)

    4
    Figure 4: Transverse momentum of the Higgs boson as measured in the Hyy decay, and compared to the Standard model predictions. (Image: ATLAS Collaboration/CERN)

    Links

    Measurement of the Higgs boson coupling properties in the H→ZZ→4l decay channel at 13 TeV with the ATLAS detector (ATLAS-CONF-2017-043): link coming soon
    Measurements of Higgs boson properties in the diphoton decay channel with 36.1 fb−1 pp collision data at the center-of-mass energy of 13 TeV with the ATLAS detector (ATLAS-CONF-2017-045): link coming soon
    Combined measurements of Higgs boson production and decay in the H→ZZ*→4ℓ and H→γγ channels using 13 TeV pp collision data collected with the ATLAS experiment (ATLAS-CONF-2017-047): link coming soon
    EPS 2017 presentation by Ruchi Gupta: Measurement of the Higgs boson couplings and properties in the diphoton, ZZ and WW decay channels using the ATLAS detector : and Tamara Vazquez Schroeder Determination of the Higgs boson properties with the ATLAS detector
    See also the full lists of ATLAS Conference Notes and ATLAS Physics Papers.

    See the full article here .

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  • richardmitnick 8:35 pm on June 28, 2017 Permalink | Reply
    Tags: , CERN ATLAS, , Katie Dunne, , , , ,   

    From LBNL: Women in STEM “Berkeley Lab Intern Finds Her Way in Particle Physics” Katie Dunne 

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    Berkeley Lab

    June 27, 2017
    Theresa Duque
    tnduque@lbl.gov
    (510) 495-2418

    1
    Intern Katherine Dunne with mentor Maurice Garcia-Sciveres. (Credit: Marilyn Chung/Berkeley Lab)

    As a high school student in Birmingham, Alabama, Berkeley Lab Undergraduate Research (BLUR) intern Katie Dunne first dreamed of becoming a physicist after reading Albert Einstein’s biography, but didn’t know anyone who worked in science. “I felt like the people who were good at math and science weren’t my friends,” she said. So when it came time for college, she majored in English, and quickly grew dissatisfied because it wasn’t challenging enough. Eventually, she got to know a few engineers, but none of them were women, she recalled.

    She still kept physics in the back of her mind until she read an article about “The First Lady of Physics,” Chien-Shiung Wu, an experimental physicist who worked on the Manhattan Project, and later designed the “Wu experiment,” which proved that the conservation of parity is violated by weak interactions. “Two male theorists who proposed parity violation won the 1957 Nobel Prize in physics, and Wu did not,” Dunne said. “When I read about her, I decided that that’s what I want to do – design experiments.”

    So she put physics front and center, and about four years ago, transferred as a physics major to the City College of San Francisco. “With Silicon Valley nearby, there are many opportunities here to get work experience in instrumentation and electrical engineering,” Dunne said. In the summers of 2014 and 2015, she landed internships in the Human Factors division at NASA Ames Research Center in Mountain View, where she streamlined the development of a printed circuit board for active infrared illumination.

    But it wasn’t until she took a class in modern physics when she discovered her true passion – particle physics. “When we got to quantum physics, it was great. Working on the problems of quantum physics is exciting,” she said. “It’s so elegant and dovetails with math. It’s the ultimate mystery because we can’t observe quantum behavior.”

    When it came time to apply for her next summer internship in 2016, instead of reapplying for a position at NASA, she googled “ATLAS,” the name of a 7,000-ton detector for the Large Hadron Collider (LHC). Her search drummed up an article about Beate Heinemann, who, at the time, was a researcher with dual appointments at UC Berkeley and Berkeley Lab and was deputy spokesperson of the ATLAS collaboration. (Heinemann is also one of the 20 percent of female physicists working on the ATLAS experiment.)

    CERN/ATLAS detector

    When Dunne contacted Heinemann to ask if she would consider her for an internship, she suggested that she contact Maurice Garcia-Sciveres, a physicist at Berkeley Lab whose research specializes in pixel detectors for ATLAS, and who has mentored many students interested in instrumentation.

    Garcia-Sciveres invited Dunne to a meeting so she could see the kind of work that they do. “I could tell I would get a lot of hands-on experience,” she said. So she applied for her first internship with Garcia-Sciveres through the Community College Internship (CCI) program – which, like the BLUR internship program, is managed by Workforce Development & Education at Berkeley Lab – and started to work with his team on building prototype integrated circuit (IC) test systems for ATLAS as part of the High Luminosity Large Hadron Collider (HL-LHC) Project, an international collaboration headed by CERN to increase the LHC’s luminosity (rate of collisions) by a factor of 10 by 2020.

    3
    A quad module with a printed circuit board (PCB) for power and data interface to four FE-I4B chips. Dunne designed the PCB. (Credit: Katie Dunne/Berkeley Lab)

    “For the ATLAS experiment, we work with the Engineering Division to build custom electronics and integrated circuits for silicon detectors. Our work is focused on improving the operation, testing, and debugging of these ICs,” said Garcia-Sciveres.

    During Dunne’s first internship, she analyzed threshold scans for an IC readout chip, and tested their radiation hardness – or threshold for tolerating increasing radiation doses – at the Lab’s 88-Inch Cyclotron and at SLAC National Accelerator Laboratory. “Berkeley Lab is a unique environment for interns. They throw you in, and you learn on the job. The Lab gives students opportunities to make a difference in the field they’re working in,” she said.

    For Garcia-Sciveres, it didn’t take long for Dunne to prove she could make a difference for his team. Just after her first internship at Berkeley Lab, the results from her threshold analysis made their debut as data supporting his presentation at the 38th International Conference on High Energy Physics (ICHEP) in August 2016. “The results were from her measurements,” he said. “This is grad student-level work she’s been doing. She’s really good.”

    5
    Katie Dunne delivers a poster presentation in spring 2017. (Credit: Marilyn Chung/Berkeley Lab)

    After the conference, Garcia-Sciveres asked Dunne to write the now published proceedings (he and the other authors provided her with comments and suggested wording). And this past January, Dunne presented “Results of FE65-P2 Stability Tests for the High Luminosity LHC Upgrade” during the “HL-LHC, BELLE2, Future Colliders” session of the American Physical Society (APS) Meeting in Washington, D.C.

    This summer, for her third and final internship at the Lab, Dunne is working on designing circuit boards needed for the ATLAS experiment, and assembling and testing prototype multi-chip modules to evaluate system performance. She hopes to continue working on ATLAS when she transfers to UC Santa Cruz as a physics major in the fall, and would like to get a Ph.D. in physics one day. “I love knowing that the work I do matters. My internships and work experience as a research assistant at Berkeley Lab have made me more confident in the work I’m doing, and more passionate about getting things done and sharing my results,” she said.

    Go here for more information about internships hosted by Workforce Development & Education at Berkeley Lab, or contact them at education@lbl.gov.

    See the full article here .

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  • richardmitnick 5:31 pm on June 27, 2017 Permalink | Reply
    Tags: , CERN ATLAS, , How to run a particle detector, , ,   

    From ATLAS: “How to run a particle detector” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    23rd June 2017
    Karola Dette

    5
    Karola Dette is a Post Doctoral Fellow at the University of Toronto, working on the tracking system upgrade for ATLAS’ high-luminosity setup. She joined the ATLAS collaboration in 2012 as a Master’s student with the University of Dortmund followed by a PhD for which she moved to CERN. During her PhD she became involved in the operation of the ATLAS detector, acting as shift leader and shifter/expert for the pixel detector.

    1
    1
    3
    Control room images. No image captions or credits.

    If you are interested in particle physics, you probably hear a lot about the huge amount of data that is recorded by experiments like ATLAS. But where does this data come from? Roughly speaking: first you have to plan, build and maintain an experiment and in the end you need people to analyse the data you’ve recorded. But what happens in between? What happens in the day-to-day life of people in the ATLAS control room, who are responsible for keeping all that great data coming?

    24 hours a day, 7 days a week, people are working at the ATLAS control room to keep the detector healthy and running. We have shifters who constantly check the subsystems of ATLAS, namely the tracking, calorimeter and muon systems. Then there are shifters who take care of the data recording itself, starting and stopping the data-taking, making sure we have the correct recording rates and monitoring the raw data that comes in. And then there is myself, acting as the shift leader.

    What does a shift leader do? Well, I’d say it is mainly talking to people. I am responsible for making sure that all the other shifters are communicating all the time to ensure that no problem goes unnoticed. If the data quality shifter sees any deviation from the expected output, she will inform me and we can follow up on what is causing this with the shifter of the affected subsystem or experts on call. This way we make sure that all the data we record is of highest quality and we don’t lose data that we could have recorded.

    That week, though, there were no stable beam collisions and therefore no “normal” data-taking going on, so what were we doing during a shift?

    When I started my shift at 3pm on 10 May 2017, the LHC was just ramping up its energy and ATLAS was already in data recording mode, ready to receive the first collisions in 2017. The first thing on your list as shift leader is to check if your crew is complete and, as you can see from the pictures of that day, we had our fair share of women working in the control room. [I have a series, Women in STEM, where I feature women one at a time. Why? Because women, especially in Physics, but I assume in all of the sciences, do not get a fair shake, and we are losing their talents.]

    _____________________________________________________________________

    24 hours a day, 7 days a week, people are working at the ATLAS control room to keep the detector healthy and running.
    _____________________________________________________________________

    After checking that all systems were working faultlessly and that the recording settings were correct, we had to wait for the LHC to find the right beam position to provide collisions in ATLAS. Only half an hour after they started to fine-tune the beams, we had the first collisions of 2017! This is an important milestone for the whole community and you can easily see how excited everybody gets by events like this by looking at the reaction of the shift crew. Everybody got up to take pictures of the event displays, showing the particle tracks of those first collisions. It feels a bit as if you are six years old again, it’s your birthday and you just got an amazing gift.

    After the beams were dumped, the data-taking was stopped to give our experts time to do stand-alone work with their systems. During this time, the experts are able to do calibrations, update parts of the software or run tests to verify former updates. My job between beam fills is mainly to take care that everybody sticks to the given time schedule. But since there is no time-crucial data-taking going on, it is a bit more relaxed than during times where we have colliding beams in the LHC. Therefore, I sometimes use this time to inform the public about what is going on with the LHC and ATLAS via my Twitter and Instagram accounts.

    See the full article here .

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