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Open Access Publications from the University of California

Scholarly Works (51 results)

  • Article
  • Peer Reviewed
UC Santa Cruz Previously Published Works (2013)
A search for resonant diboson production using a data sample corresponding to 4:7 fb–1of integrated luminosity collected by the ATLAS experiment at the Large Hadron Collider in pp collisions at √s = 7 TeV is presented. The search for a narrow resonance in the WW or WZ mass distribution is conducted in a final state with an electron or a muon, missing transverse momentum, and at least two jets. No significant excess is observed and limits are set using three benchmark models: WW resonance masses below 940 and 710 GeV are excluded at 95% confidence level for spin-2 Randall–Sundrum and bulk Randall–Sundrum gravitons, respectively; WZ resonance masses below 950 GeV are excluded at 95% confidence level for a spin-1 extended gauge model W′ boson.
    Cover page: Search for resonant diboson production in the WW/WZ→ℓνjj decay channels with the ATLAS detector at s=7 TeVCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UC Santa Cruz Previously Published Works (2012)
    Measurements are presented of the properties of high transverse momentum jets, produced in proton-proton collisions at a center-of-mass energy of √s=7TeV. The data correspond to an integrated luminosity of 35pb -1 and were collected with the ATLAS detector in 2010. Jet mass, width, eccentricity, planar flow and angularity are measured for jets reconstructed using the anti-kt algorithm with distance parameters R=0.6 and 1.0, with transverse momentum pT>300GeV and pseudorapidity |η|<2. The measurements are compared to the expectations of Monte Carlo generators that match leading-logarithmic parton showers to leading-order, or next-to-leading-order, matrix elements. The generators describe the general features of the jets, although discrepancies are observed in some distributions. © 2012 CERN, for the ATLAS Collaboration Published by the American Physical Society under the terms of the http://creativecommons. org/licenses/by/3.0/ Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
      Cover page: ATLAS measurements of the properties of jets for boosted particle searchesCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2012)
      We present an update of a search for supersymmetry in final states containing jets, missing transverse momentum, and one isolated electron or muon, using 1.04fb -1 of proton-proton collision data at √s=7TeV recorded by the ATLAS experiment at the LHC in the first half of 2011. The analysis is carried out in four distinct signal regions with either three or four jets and variations on the (missing) transverse momentum cuts, resulting in optimized limits for various supersymmetry models. No excess above the standard model background expectation is observed. Limits are set on the visible cross section of new physics within the kinematic requirements of the search. The results are interpreted as limits on the parameters of the minimal supergravity framework, limits on cross sections of simplified models with specific squark and gluino decay modes, and limits on parameters of a model with bilinear R-parity violation. © 2012 CERN.
        Cover page: Search for supersymmetry in final states with jets, missing transverse momentum and one isolated lepton in s=7 TeV pp collisions using 1 fb-1 of ATLAS dataCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2012)
        The ATLAS detector is used to search for excited leptons in the electromagnetic radiative decay channel *→γ. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 2.05fb-1. No evidence for excited leptons is found, and limits are set on the compositeness scale Λ as a function of the excited lepton mass m *. In the special case where Λ=m *, excited electron and muon masses below 1.87 TeV and 1.75 TeV are excluded at 95% C.L., respectively. © 2012 CERN.
          Cover page: Search for excited leptons in proton-proton collisions at s=7 TeV with the ATLAS detectorCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UC Santa Cruz Previously Published Works (2013)
          Using 1.8 fb-1 of pp collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the Large Hadron Collider, we present measurements of the production cross sections of Υ(1S,2S,3S) mesons. Υ mesons are reconstructed using the dimuon decay mode. Total production cross sections for pT<70 GeV and in the rapidity interval |yΥ|<2.25 are measured to be, 8.01±0.02±0.36±0.31 nb, 2.05±0.01±0.12±0.08 nb, and 0.92±0.01±0. 07±0.04 nb, respectively, with uncertainties separated into statistical, systematic, and luminosity measurement effects. In addition, differential cross section times dimuon branching fractions for Υ(1S), Υ(2S), and Υ(3S) as a function of Υ transverse momentum pT and rapidity are presented. These cross sections are obtained assuming unpolarized production. If the production polarization is fully transverse or longitudinal with no azimuthal dependence in the helicity frame, the cross section may vary by approximately ±20%. If a nontrivial azimuthal dependence is considered, integrated cross sections may be significantly enhanced by a factor of 2 or more. We compare our results to several theoretical models of Υ meson production, finding that none provide an accurate description of our data over the full range of Υ transverse momenta accessible with this data set.
            Cover page: Measurement of upsilon production in 7 TeV pp collisions at ATLASCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Santa Cruz Previously Published Works (2012)
            A search for the Higgs boson has been performed in the H→WW(*)→ℓ(+)νℓ(-)ν[over ¯] channel (ℓ=e/μ) with an integrated luminosity of 2.05 fb(-1) of pp collisions at √s=7 TeV collected with the ATLAS detector at the Large Hadron Collider. No significant excess of events over the expected background is observed and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 110 GeV
              Cover page: Search for the Higgs Boson in the H→WW(*)→l+νl-ν¯ Decay Channel in pp Collisions at s=7 TeV with the ATLAS DetectorCreative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UC Berkeley Previously Published Works (2018)
              A search for long-lived, massive particles predicted by many theories beyond the Standard Model is presented. The search targets final states with large missing transverse momentum and at least one high-mass displaced vertex with five or more tracks, and uses 32.8 fb$^{-1}$ of $\sqrt{s}$ = 13 TeV $pp$ collision data collected by the ATLAS detector at the LHC. The observed yield is consistent with the expected background. The results are used to extract 95\% CL exclusion limits on the production of long-lived gluinos with masses up to 2.37 TeV and lifetimes of $\mathcal{O}(10^{-2})$-$\mathcal{O}(10)$ ns in a simplified model inspired by Split Supersymmetry.
                • Article
                • Peer Reviewed
                UC Irvine Previously Published Works (2011)
                Measurements of charged particle distributions, sensitive to the underlying event, have been performed with the ATLAS detector at the LHC. The measurements are based on data collected using a minimum-bias trigger to select proton-proton collisions at center-of-mass energies of 900 GeV and 7 TeV. The "underlying event" is defined as those aspects of a hadronic interaction attributed not to the hard scattering process, but rather to the accompanying interactions of the rest of the proton. Three regions are defined in azimuthal angle with respect to the highest transverse momentum charged particle in the event, such that the region transverse to the dominant momentum-flow is most sensitive to the underlying event. In each of these regions, distributions of the charged particle multiplicity, transverse momentum density, and average pT are measured. The data show generally higher underlying event activity than that predicted by Monte Carlo models tuned to pre-LHC data. © 2011 American Physical Society.
                  Cover page: Measurement of underlying event characteristics using charged particles in pp collisions at s=900 GeV and 7 TeV with the ATLAS detectorCreative Commons 'BY' version 4.0 license
                  • Article
                  • Peer Reviewed
                  UC Santa Cruz Previously Published Works (2012)
                  This paper presents a search for a new heavy particle produced in association with a top or antitop quark. Two models in which the new heavy particle is a color singlet or a color triplet are considered, decaying, respectively, to t̄q or tq, leading to a resonance within the tt̄+jets signature. The full 2011 ATLAS pp collision data set from the LHC (4.7fb -1) is used to search for tt̄ events produced in association with jets, in which one of the W bosons from the top quarks decays leptonically and the other decays hadronically. The data are consistent with the Standard Model expectation, and a new particle with mass below 430 Gev for both W ′ boson and color triplet models is excluded at 95% confidence level, assuming unit right-handed coupling. © 2012 CERN.
                    Cover page: Search for resonant top quark plus jet production in tt¯+jets events with the ATLAS detector in pp collisions at s=7 TeVCreative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    UC Irvine Previously Published Works (2013)
                    A search has been performed for photons originating in the decay of a neutral long-lived particle, exploiting the capabilities of the ATLAS electromagnetic calorimeter to make precise measurements of the flight direction of photons, as well as the calorimeter's excellent time resolution. The search has been made in the diphoton plus missing transverse energy final state, using the full data sample of 4.8 fb-1 of 7 TeV proton-proton collisions collected in 2011 with the ATLAS detector at the LHC. No excess is observed above the background expected from Standard Model processes. The results are used to set exclusion limits in the context of gauge mediated supersymmetry breaking models, with the lightest neutralino being the next-to-lightest supersymmetric particle and decaying with a lifetime in excess of 0.25 ns into a photon and a gravitino. © 2013 CERN.
                      Cover page: Search for nonpointing photons in the diphoton and ETmiss final state in s=7 TeV proton-proton collisions using the ATLAS detectorCreative Commons 'BY' version 4.0 license
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