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Open Access Publications from the University of California

Scholarly Works (246 results)

  • Article
  • Peer Reviewed
LBL Publications (2000)
A new precision measurement of the Ξ0 mass has been performed at the NA48 experiment at the CERN SPS. The value obtained is [1314.82±0.06 (stat.) ±0.2 (syst.)] MeV/c2. The branching ratios of Xi;0 radiative decays have been measured as: Br(Ξ0 → Λγ) = [1.90 ± 0.34(stat.) ± 0.19(syst.)] · 10-3 and Br(Ξ0 → ∑0γ) = [3.14 ± 0.76(stat.) ± 0.32(syst.)] · 10-3.
    Cover page: Precision measurement of the Ξ<sup>0</sup> mass and the branching ratios of the decays Ξ<sup>0</sup> → Λγ and Ξ<sup>0</sup> → ∑<sup>0</sup>γ
    • Article
    • Peer Reviewed
    UC Santa Cruz Previously Published Works (2012)
    This Letter presents a search for pair production of heavy down-type quarks decaying via b' → Wt in the lepton + jets channel, as b'b' → W- tW+ t → bbW+ W- W+ W- → l± νbbqqqqqq. In addition to requiring exactly one lepton, large missing transverse momentum, and at least six jets, the invariant mass of nearby jet pairs is used to identify high transverse momentum W bosons. In data corresponding to an integrated luminosity of 1.04  fb(-1) from pp collisions at sqrt[s] = 7  TeV recorded with the ATLAS detector, a heavy down-type quark with mass less than 480 GeV can be excluded at the 95% confidence level.
      Cover page: Search for Down-Type Fourth Generation Quarks with the ATLAS Detector in Events with One Lepton and Hadronically Decaying W BosonsCreative Commons 'BY' version 4.0 license
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      • Peer Reviewed
      UC Davis Previously Published Works (2012)
      New metastable massive particles with electric and colour charge are features of many theories beyond the Standard Model. A search is performed for long-lived gluino-based R-hadrons with the ATLAS detector at the LHC using a data sample corresponding to an integrated luminosity of 31 pb−1. We search for evidence of particles that have come to rest in the ATLAS detector and decay at some later time during the periods in the LHC bunch structure without proton–proton collisions. No significant deviations from the expected backgrounds are observed, and a cross-section limit is set. It can be interpreted as excluding gluino-based R-hadrons with masses less than 341 GeV at the 95 % C.L., for lifetimes from 10−5to 103seconds and a neutralino mass of 100 GeV.
        Cover page: Search for decays of stopped, long-lived particles from 7 TeV pp collisions with the ATLAS detectorCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC Santa Cruz Previously Published Works (2012)
        A search for the Standard Model Higgs boson decaying into a pair of τ leptons is reported. The analysis is based on a data sample of proton-proton collisions collected by the ATLAS experiment at the LHC and corresponding to an integrated luminosity of 4.7fb-1. No significant excess over the expected background is observed in the Higgs boson mass range of 100-150 GeV. The observed (expected) upper limits on the cross section times the branching ratio for H → τ+τ- are found to be between 2.9 (3.4) and 11.7 (8.2) times the Standard Model prediction for this mass range.
          Cover page: Search for the Standard Model Higgs boson in the H → τ+τ− decay mode in pp collisions with ATLASCreative Commons 'BY' version 4.0 license
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          • Peer Reviewed
          UC Santa Cruz Previously Published Works (2012)
          A search for production of supersymmetric particles in final states containing jets, missing transverse momentum, and at least one hadronically decaying τ lepton is presented. The data were recorded by the ATLAS experiment in s=7TeV proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 2.05fb-1 of data. The results are interpreted in the context of gauge mediated supersymmetry breaking models with Mmess=250TeV, N5=3, μ>0, and Cgrav=1. The production of supersymmetric particles is excluded at 95% C.L. up to a supersymmetry breaking scale Λ=30TeV, independent of tanβ, and up to Λ=43TeV for large tanβ. © 2012.
            Cover page: Search for supersymmetry with jets, missing transverse momentum and at least one hadronically decaying τ lepton in proton–proton collisions at s=7&nbsp;TeV with the ATLAS detectorCreative Commons 'BY' version 4.0 license
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            • Peer Reviewed
            UC Santa Cruz Previously Published Works (2012)
            This Letter describes a model-independent search for the production of new resonant states in photon+jet events in 2.11 fb(-1) of proton-proton collisions at √s=7 TeV. We compare the photon+jet mass distribution to a background model derived from data and find consistency with the background-only hypothesis. Given the lack of evidence for a signal, we set 95% credibility level limits on generic Gaussian-shaped signals and on a benchmark excited-quark (q*) model, excluding 2 TeV Gaussian resonances with cross section times branching fraction times acceptance times efficiency near 5 fb and excluding q* masses below 2.46 TeV, respectively.
              Cover page: Search for Production of Resonant States in the Photon-Jet Mass Distribution Using pp Collisions at s=7 TeV Collected by the ATLAS DetectorCreative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UC Irvine Previously Published Works (2012)
              A search for direct pair production of supersymmetric top squarks (t(1)) is presented, assuming the t(1) decays into a top quark and the lightest supersymmetric particle, χ(1)(0), and that both top quarks decay to purely hadronic final states. A total of 16 (4) events are observed compared to a predicted standard model background of 13.5(-3.6)(+3.7)(4.4(-1.3)(+1.7)) events in two signal regions based on ∫Ldt = 4.7 fb(-1) of pp collision data taken at sqrt[s] = 7 TeV with the ATLAS detector at the LHC. An exclusion region in the t(1) versus χ(1)(0) mass plane is evaluated: 370
                Cover page: Search for a Supersymmetric Partner to the Top Quark in Final States with Jets and Missing Transverse Momentum at s=7 TeV with the ATLAS DetectorCreative Commons 'BY' version 4.0 license
                • Article
                • Peer Reviewed
                UC Santa Cruz Previously Published Works (2012)
                This work presents a new inclusive search for supersymmetry (SUSY) by the ATLAS experiment at the LHC in proton-proton collisions at a center-of-mass energy √s=7TeV in final states with jets, missing transverse momentum and one or more isolated electrons and/or muons. The search is based on data from the full 2011 data-taking period, corresponding to an integrated luminosity of 4.7fb-1. Single-lepton and multilepton channels are treated together in one analysis. An increase in sensitivity is obtained by simultaneously fitting the number of events in statistically independent signal regions, and the shapes of distributions within those regions. A dedicated signal region is introduced to be sensitive to decay cascades of SUSY particles with small mass differences ("compressed SUSY"). Background uncertainties are constrained by fitting to the jet-multiplicity distribution in background control regions. Observations are consistent with Standard Model expectations, and limits are set or extended on a number of SUSY models. © 2012 CERN.
                  Cover page: Further search for supersymmetry at s=7 TeV in final states with jets, missing transverse momentum, and isolated leptons with the ATLAS detectorCreative Commons 'BY' version 4.0 license
                  • Article
                  • Peer Reviewed
                  UC Santa Cruz Previously Published Works (2013)
                  The measurement of the jet energy resolution is presented using data recorded with the ATLAS detector in proton-proton collisions at [Formula: see text]. The sample corresponds to an integrated luminosity of 35 pb-1. Jets are reconstructed from energy deposits measured by the calorimeters and calibrated using different jet calibration schemes. The jet energy resolution is measured with two different in situ methods which are found to be in agreement within uncertainties. The total uncertainties on these measurements range from 20 % to 10 % for jets within |y|<2.8 and with transverse momenta increasing from 30 GeV to 500 GeV. Overall, the Monte Carlo simulation of the jet energy resolution agrees with the data within 10 %.
                    Cover page: Jet energy resolution in proton-proton collisions at recorded in 2010 with the ATLAS detectorCreative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    UC Santa Cruz Previously Published Works (2013)
                    A search for neutral Higgs bosons of the Minimal Supersymmetric Standard Model (MSSM) is reported. The analysis is based on a sample of proton-proton collisions at a centre-of-mass energy of 7TeV recorded with the ATLAS detector at the Large Hadron Collider. The data were recorded in 2011 and correspond to an integrated luminosity of 4.7 fb-1 to 4.8 fb-1. Higgs boson decays into oppositely-charged muon or τ lepton pairs are considered for final states requiring either the presence or absence of b-jets. No statistically significant excess over the expected background is observed and exclusion limits at the 95% confidence level are derived. The exclusion limits are for the production cross-section of a generic neutral Higgs boson, φ, as a function of the Higgs boson mass and for h/A/H production in the MSSM as a function of the parameters mA and tan β in the mhmax scenario for mA in the range of 90GeV to 500 GeV. Copyright CERN.
                      Cover page: Search for the neutral Higgs bosons of the minimal supersymmetric standard model in pp collisions at TeV with the ATLAS detectorCreative Commons 'BY' version 4.0 license
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