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Open Access Publications from the University of California

Scholarly Works (215 results)

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Recent Work (2014)
© 2014, The Author(s). This report of the BOOST2012 workshop presents the results of four working groups that studied key aspects of jet substructure. We discuss the potential of first-principle QCD calculations to yield a precise description of the substructure of jets and study the accuracy of state-of-the-art Monte Carlo tools. Limitations of the experiments’ ability to resolve substructure are evaluated, with a focus on the impact of additional (pile-up) proton proton collisions on jet substructure performance in future LHC operating scenarios. A final section summarizes the lessons learnt from jet substructure analyses in searches for new physics in the production of boosted top quarks.
    Cover page: Boosted objects and jet substructure at the LHC. Report of BOOST2012, held at IFIC Valencia, 23rd–27th of July 2012
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    UC Santa Cruz Previously Published Works (2015)
    Measurements of the total and differential cross sections of Higgs boson production are performed using 20.3  fb^{-1} of pp collisions produced by the Large Hadron Collider at a center-of-mass energy of sqrt[s]=8  TeV and recorded by the ATLAS detector. Cross sections are obtained from measured H→γγ and H→ZZ^{*}→4ℓ event yields, which are combined accounting for detector efficiencies, fiducial acceptances, and branching fractions. Differential cross sections are reported as a function of Higgs boson transverse momentum, Higgs boson rapidity, number of jets in the event, and transverse momentum of the leading jet. The total production cross section is determined to be σ_{pp→H}=33.0±5.3 (stat)±1.6 (syst)  pb. The measurements are compared to state-of-the-art predictions.
      Cover page: Measurements of the Total and Differential Higgs Boson Production Cross Sections Combining the H→γγ and H→ZZ^{*}→4ℓ Decay Channels at sqrt[s]=8  TeV with the ATLAS Detector.Creative Commons 'BY' version 4.0 license
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      UC Santa Cruz Previously Published Works (2013)
      Measurements of the variation of inclusive jet suppression as a function of relative azimuthal angle, Δφ, with respect to the elliptic event plane provide insight into the path-length dependence of jet quenching. ATLAS has measured the Δφ dependence of jet yields in 0.14 nb(-1) of √(s(NN))=2.76 TeV Pb+Pb collisions at the LHC for jet transverse momenta p(T)>45 GeV in different collision centrality bins using an underlying event subtraction procedure that accounts for elliptic flow. The variation of the jet yield with Δφ was characterized by the parameter, v(2)(jet), and the ratio of out-of-plane (Δφ~π/2) to in-plane (Δφ~0) yields. Nonzero v(2)(jet) values were measured in all centrality bins for p(T)<160 GeV. The jet yields are observed to vary by as much as 20% between in-plane and out-of-plane directions.
        Cover page: Measurement of the azimuthal angle dependence of inclusive jet yields in Pb+Pb collisions at √(sNN)=2.76 TeV with the ATLAS detector.Creative Commons 'BY' version 4.0 license
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        • Peer Reviewed
        Recent Work (2017)
        High-precision measurements by the ATLAS Collaboration are presented of inclusive W+→ℓ+ν , W-→ℓ-ν¯ and Z/γ∗→ℓℓ ( ℓ=e,μ ) Drell-Yan production cross sections at the LHC. The data were collected in proton-proton collisions at s=7TeV with an integrated luminosity of 4.6fb-1 . Differential W+ and W- cross sections are measured in a lepton pseudorapidity range |ηℓ|<2.5 . Differential Z/γ∗ cross sections are measured as a function of the absolute dilepton rapidity, for |yℓℓ|<3.6 , for three intervals of dilepton mass, mℓℓ , extending from 46 to 150GeV . The integrated and differential electron- and muon-channel cross sections are combined and compared to theoretical predictions using recent sets of parton distribution functions. The data, together with the final inclusive e±p scattering cross-section data from H1 and ZEUS, are interpreted in a next-to-next-to-leading-order QCD analysis, and a new set of parton distribution functions, ATLAS-epWZ16, is obtained. The ratio of strange-to-light sea-quark densities in the proton is determined more accurately than in previous determinations based on collider data only, and is established to be close to unity in the sensitivity range of the data. A new measurement of the CKM matrix element |Vcs| is also provided.
          Cover page: Precision measurement and interpretation of inclusive W+ , W- and Z/γ∗ production cross sections with the ATLAS detector.
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          UC Santa Cruz Previously Published Works (2015)
          Studies of the spin and parity quantum numbers of the Higgs boson in the [Formula: see text] final state are presented, based on proton-proton collision data collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb[Formula: see text] at a centre-of-mass energy of [Formula: see text] TeV. The Standard Model spin-parity [Formula: see text] hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the Standard-Model-like Higgs boson and CP-even ([Formula: see text]) or CP-odd ([Formula: see text]) Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios.
            Cover page: Determination of spin and parity of the Higgs boson in the [Formula: see text] decay channel with the ATLAS detector.Creative Commons 'BY' version 4.0 license
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