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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Article
  • Peer Reviewed
UC San Diego Previously Published Works (2018)
Events with no charged particles produced between the two leading jets are studied in proton-proton collisions at s=7 TeV . The jets were required to have transverse momentum pTjet>40 GeV and pseudorapidity 1.5<|ηjet|<4.7 , and to have values of ηjet with opposite signs. The data used for this study were collected with the CMS detector during low-luminosity running at the LHC, and correspond to an integrated luminosity of 8 pb-1 . Events with no charged particles with pT>0.2 GeV in the interval -1<η<1 between the jets are observed in excess of calculations that assume no color-singlet exchange. The fraction of events with such a rapidity gap, amounting to 0.5-1% of the selected dijet sample, is measured as a function of the pT of the second-leading jet and of the rapidity separation between the jets. The data are compared to previous measurements at the Tevatron, and to perturbative quantum chromodynamics calculations based on the Balitsky-Fadin-Kuraev-Lipatov evolution equations, including different models of the non-perturbative gap survival probability.
    Cover page: Study of dijet events with a large rapidity gap between the two leading jets in pp collisions at s=7TeVCreative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2017)
    A measurement is presented of the triple-differential dijet cross section at a centre-of-mass energy of 8 TeV using 19.7 fb-1 of data collected with the CMS detector in proton-proton collisions at the LHC. The cross section is measured as a function of the average transverse momentum, half the rapidity separation, and the boost of the two leading jets in the event. The cross section is corrected for detector effects and compared to calculations in perturbative quantum chromodynamics at next-to-leading order accuracy, complemented with electroweak and nonperturbative corrections. New constraints on parton distribution functions are obtained and the inferred value of the strong coupling constant is αS(MZ)=0.1199±0.0015(exp)-0.0020+0.0031(theo) , where MZ is the mass of the Z boson.
      Cover page: Measurement of the triple-differential dijet cross section in proton-proton collisions at s=8TeV and constraints on parton distribution functionsCreative Commons 'BY' version 4.0 license
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2017)
      A measurement of the top quark mass is reported in events containing a single top quark produced via the electroweak t channel. The analysis is performed using data from proton-proton collisions collected with the CMS detector at the LHC at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 19.7 fb[Formula: see text]. Top quark candidates are reconstructed from their decay to a [Formula: see text] boson and a b quark, with the [Formula: see text] boson decaying leptonically to a muon and a neutrino. The final state signature and kinematic properties of single top quark events in the t channel are used to enhance the purity of the sample, suppressing the contribution from top quark pair production. A fit to the invariant mass distribution of reconstructed top quark candidates yields a value of the top quark mass of [Formula: see text]. This result is in agreement with the current world average, and represents the first measurement of the top quark mass in event topologies not dominated by top quark pair production, therefore contributing to future averages with partially uncorrelated systematic uncertainties and a largely uncorrelated statistical uncertainty.
        Cover page: Measurement of the top quark mass using single top quark events in proton-proton collisions at s=8 TeVCreative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2018)
        A study of the associated production of a Z boson and a charm quark jet ( Z+c ), and a comparison to production with a b quark jet ( Z+b ), in pp collisions at a centre-of-mass energy of 8 TeV are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7 fb-1 , collected with the CMS detector at the CERN LHC. The Z boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of c or b flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with pTℓ>20GeV , |ηℓ|<2.1 , 7125GeV and |ηjet|<2.5 . The Z+c production cross section is measured to be σ(pp→Z+c+X)B(Z→ℓ+ℓ-)=8.8±0.5(stat)±0.6(syst)pb . The ratio of the Z+c and Z+b production cross sections is measured to be σ(pp→Z+c+X)/σ(pp→Z+b+X)=2.0±0.2(stat)±0.2(syst) . The Z+c production cross section and the cross section ratio are also measured as a function of the transverse momentum of the Z boson and of the heavy flavour jet. The measurements are compared with theoretical predictions.
          Cover page: Measurement of associated Z + charm production in proton–proton collisions at s=8TeVCreative Commons 'BY' version 4.0 license
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2017)
          A search is presented for an excess of events with heavy-flavor quark pairs ( tt¯ and bb¯ ) and a large imbalance in transverse momentum in data from proton-proton collisions at a center-of-mass energy of 13 TeV . The data correspond to an integrated luminosity of 2.2 fb-1 collected with the CMS detector at the CERN LHC. No deviations are observed with respect to standard model predictions. The results are used in the first interpretation of dark matter production in tt¯ and bb¯ final states in a simplified model. This analysis is also the first to perform a statistical combination of searches for dark matter produced with different heavy-flavor final states. The combination provides exclusions that are stronger than those achieved with individual heavy-flavor final states.
            Cover page: Search for dark matter produced in association with heavy-flavor quark pairs in proton-proton collisions at s=13TeVCreative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2017)
            The first measurement of the jet mass mjet of top quark jets produced in tt¯ events from pp collisions at s√=8 TeV is reported for the jet with the largest transverse momentum pT in highly boosted hadronic top quark decays. The data sample, collected with the CMS detector, corresponds to an integrated luminosity of 19.7fb−1. The measurement is performed in the lepton+jets channel in which the products of the semileptonic decay t→bW with W→ℓν where ℓ is an electron or muon, are used to select tt¯ events with large Lorentz boosts. The products of the fully hadronic decay t→bW with W→qq¯¯¯′ are reconstructed using a single Cambridge–Aachen jet with distance parameter R=1.2, and pT>400 GeV. The tt¯ cross section as a function of mjet is unfolded at the particle level and is used to test the modelling of highly boosted top quark production. The peak position of the mjet distribution is sensitive to the top quark mass mt, and the data are used to extract a value of mt to assess this sensitivity.
              Cover page: Measurement of the jet mass in highly boosted tt¯ events from pp collisions at s√=8 TeV
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