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Open Access Publications from the University of California

Scholarly Works (16 results)

  • Article
  • Peer Reviewed
UC Riverside Previously Published Works (2015)
We present the final combination of CDF and D0 measurements of cross sections for single-top-quark production in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. The data correspond to total integrated luminosities of up to 9.7 fb^{-1} per experiment. The t-channel cross section is measured to be σ_{t}=2.25_{-0.31}^{+0.29} pb. We also present the combinations of the two-dimensional measurements of the s- vs t-channel cross section. In addition, we give the combination of the s+t channel cross section measurement resulting in σ_{s+t}=3.30_{-0.40}^{+0.52} pb, without assuming the standard model value for the ratio σ_{s}/σ_{t}. The resulting value of the magnitude of the top-to-bottom quark coupling is |V_{tb}|=1.02_{-0.05}^{+0.06}, corresponding to |V_{tb}|>0.92 at the 95% C.L.
    Cover page: Tevatron Combination of Single-Top-Quark Cross Sections and Determination of the Magnitude of the Cabibbo-Kobayashi-Maskawa Matrix Element V_{tb}.
    • Article
    • Peer Reviewed
    Recent Work (2018)
    The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of sqrt[s]=1.96  TeV. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is A_{FB}^{tt[over ¯]}=0.128±0.025. The combined inclusive and differential asymmetries are consistent with recent standard model predictions.
      Cover page: Combined Forward-Backward Asymmetry Measurements in Top-Antitop Quark Production at the Tevatron.
      • 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 functions.
        • 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
          • Article
          • Peer Reviewed
          UC Riverside Previously Published Works (2012)
          We present a search for the standard model Higgs boson produced in association with a $Z$ boson, using up to 7.9 fb$^{-1}$ of integrated luminosity from $p\bar{p}$ collisions collected with the CDF II detector. We utilize several novel techniques, including multivariate lepton selection, multivariate trigger parametrization, and a multi-stage signal discriminant consisting of specialized functions trained to distinguish individual backgrounds. By increasing acceptance and enhancing signal discrimination, these techniques have significantly improved the sensitivity of the analysis above what was expected from a larger dataset alone. We observe no significant evidence for a signal, and we set limits on the $ZH$ production cross section. For a Higgs boson with mass 115 GeV/$c^2$, we expect (observe) a limit of 3.9 (4.8) times the standard model predicted value, at the 95% credibility level.
            Cover page: Search for the standard model Higgs boson produced in association with W and Z bosons in pp collisions at root s=7 TeV
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2017)
            Normalized double-differential cross sections for top quark pair ([Formula: see text]) production are measured in pp collisions at a centre-of-mass energy of 8[Formula: see text] with the CMS experiment at the LHC. The analyzed data correspond to an integrated luminosity of 19.7[Formula: see text]. The measurement is performed in the dilepton [Formula: see text] final state. The [Formula: see text] cross section is determined as a function of various pairs of observables characterizing the kinematics of the top quark and [Formula: see text] system. The data are compared to calculations using perturbative quantum chromodynamics at next-to-leading and approximate next-to-next-to-leading orders. They are also compared to predictions of Monte Carlo event generators that complement fixed-order computations with parton showers, hadronization, and multiple-parton interactions. Overall agreement is observed with the predictions, which is improved when the latest global sets of proton parton distribution functions are used. The inclusion of the measured [Formula: see text] cross sections in a fit of parametrized parton distribution functions is shown to have significant impact on the gluon distribution.
              Cover page: Measurement of double-differential cross sections for top quark pair production in pp collisions at [Formula: see text][Formula: see text] and impact on parton distribution functions.
              • 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=7 TeV.
                • Article
                • Peer Reviewed