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Open Access Publications from the University of California

Scholarly Works (15 results)

  • Article
  • Peer Reviewed
Recent Work (2019)
Silicon pixel detectors are at the core of the current and planned upgrade of the ATLAS experiment at the LHC. Given their close proximity to the interaction point, these detectors will be exposed to an unprecedented amount of radiation over their lifetime. The current pixel detector will receive damage from non-ionizing radiation in excess of $10^{15}$ 1 MeV ${n}_{eq}/{cm}^2$, while the pixel detector designed for the high-luminosity LHC must cope with an order of magnitude larger fluence. This paper presents a digitization model incorporating effects of radiation damage to the pixel sensors. The model is described in detail and predictions for the charge collection efficiency and Lorentz angle are compared with collision data collected between 2015 and 2017 ($\leq 10^{15}$ 1 MeV ${n}_{eq}/{cm}^2$).
    Cover page: Modelling radiation damage to pixel sensors in the ATLAS detector
    • Article
    • Peer Reviewed
    Recent Work (2019)
    © 2019, CERN for the benefit of the ATLAS collaboration. This paper presents measurements of charged-particle distributions sensitive to the properties of the underlying event in events containing a Z boson decaying into a muon pair. The data were obtained using the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of 13 Te with an integrated luminosity of 3.2fb-1. Distributions of the charged-particle multiplicity and of the charged-particle transverse momentum are measured in regions of the azimuth defined relative to the Z boson direction. The measured distributions are compared with the predictions of various Monte Carlo generators which implement different underyling event models. The Monte Carlo model predictions qualitatively describe the data well, but with some significant discrepancies.
      Cover page: Measurement of distributions sensitive to the underlying event in inclusive Z boson production in pp collisions at root s=13 TeV with the ATLAS detectorCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      Recent Work (2019)
      A measurement of jet substructure variables is presented using data collected in 2016 by the ATLAS experiment at the LHC with proton-proton collisions at $\sqrt{s}=13$ TeV. Large-radius jets groomed with the trimming and soft-drop algorithms are studied. Dedicated event selections are used to study jets produced by light quarks or gluons, and hadronically decaying top quarks and $W$ bosons. The variables measured are sensitive to pronged substructure, and therefore are typically used for tagging jets from boosted massive particles. These include the energy correlation functions and the $N$-subjettiness variables. The number of subjets and the Les Houches angularity are also considered. The distributions of the substructure variables, corrected for detector effects, are compared to the predictions of various Monte Carlo event generators. They are also compared between the large-radius jets originating from light quarks or gluons, and hadronically decaying top quarks and $W$ bosons.
        Cover page: Measurement of jet-substructure observables in top quark, W boson and light jet production in proton-proton collisions at s $$ \sqrt{s} $$ = 13 TeV with the ATLAS detectorCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        Recent Work (2019)
        © 2019, The Author(s). Narrow resonances decaying into W W, W Z or ZZ boson pairs are searched for in 139 fb−1 of proton-proton collision data at a centre-of-mass energy of s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider from 2015 to 2018. The diboson system is reconstructed using pairs of high transverse momentum, large-radius jets. These jets are built from a combination of calorimeter- and tracker-inputs compatible with the hadronic decay of a boosted W or Z boson, using jet mass and substructure properties. The search is performed for diboson resonances with masses greater than 1.3 TeV. No significant deviations from the background expectations are observed. Exclusion limits at the 95% confidence level are set on the production cross-section times branching ratio into dibosons for resonances in a range of theories beyond the Standard Model, with the highest excluded mass of a new gauge boson at 3.8 TeV in the context of mass-degenerate resonances that couple predominantly to gauge bosons.[Figure not available: see fulltext.].
          Cover page: Search for diboson resonances in hadronic final states in 139 fb−1 of pp collisions at s $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
          • Article
          • Peer Reviewed