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Open Access Publications from the University of California

Scholarly Works (38 results)

  • Article
  • Peer Reviewed
UC San Diego Previously Published Works (2021)
Collinear (small-angle) and large-angle, as well as soft and hard radiations are investigated in three-jet and Z  + two-jet events collected in proton-proton collisions at the LHC. The normalized production cross sections are measured as a function of the ratio of transverse momenta of two jets and their angular separation. The measurements in the three-jet and Z  + two-jet events are based on data collected at a center-of-mass energy of 8 TeV , corresponding to an integrated luminosity of 19.8 fb-1 . The Z  + two-jet events are reconstructed in the dimuon decay channel of the Z  boson. The three-jet measurement is extended to include s=13TeV data corresponding to an integrated luminosity of 2.3 fb-1 . The results are compared to predictions from event generators that include parton showers, multiple parton interactions, and hadronization. The collinear and soft regions are in general well described by parton showers, whereas the regions of large angular separation are often best described by calculations using higher-order matrix elements.
    Cover page: Measurements of angular distance and momentum ratio distributions in three-jet and Z + two-jet final states in pp collisions.
    • Article
    • Peer Reviewed
    LBL Publications (2023)
    The mass of the top quark is measured in 36.3fb-1 of LHC proton-proton collision data collected with the CMS detector at s=13TeV. The measurement uses a sample of top quark pair candidate events containing one isolated electron or muon and at least four jets in the final state. For each event, the mass is reconstructed from a kinematic fit of the decay products to a top quark pair hypothesis. A profile likelihood method is applied using up to four observables per event to extract the top quark mass. The top quark mass is measured to be 171.77±0.37GeV. This approach significantly improves the precision over previous measurements.
      Cover page: Measurement of the top quark mass using a profile likelihood approach with the lepton + jets final states in proton-proton collisions at s=13TeV.
      • Article
      • Peer Reviewed
      LBL Publications (2023)
      The double differential cross sections of the Drell-Yan lepton pair (ℓ+ℓ-, dielectron or dimuon) production are measured as functions of the invariant mass mℓℓ, transverse momentum pT(ℓℓ), and φη∗. The φη∗ observable, derived from angular measurements of the leptons and highly correlated with pT(ℓℓ), is used to probe the low-pT(ℓℓ) region in a complementary way. Dilepton masses up to 1TeV are investigated. Additionally, a measurement is performed requiring at least one jet in the final state. To benefit from partial cancellation of the systematic uncertainty, the ratios of the differential cross sections for various mℓℓ ranges to those in the Z mass peak interval are presented. The collected data correspond to an integrated luminosity of 36.3fb-1 of proton-proton collisions recorded with the CMS detector at the LHC at a centre-of-mass energy of 13TeV. Measurements are compared with predictions based on perturbative quantum chromodynamics, including soft-gluon resummation.
        Cover page: Measurement of the mass dependence of the transverse momentum of lepton pairs in Drell-Yan production in proton-proton collisions at s=13TeV.
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2023)
        A search is reported for pairs of light Higgs bosons (H1) produced in supersymmetric cascade decays in final states with small missing transverse momentum. A data set of LHC pp collisions collected with the CMS detector at s=13TeV and corresponding to an integrated luminosity of 138fb-1 is used. The search targets events where both H1 bosons decay into pairs that are reconstructed as large-radius jets using substructure techniques. No evidence is found for an excess of events beyond the background expectations of the standard model (SM). Results from the search are interpreted in the next-to-minimal supersymmetric extension of the SM, where a "singlino" of small mass leads to squark and gluino cascade decays that can predominantly end in a highly Lorentz-boosted singlet-like H1 and a singlino-like neutralino of small transverse momentum. Upper limits are set on the product of the squark or gluino pair production cross section and the square of the branching fraction of the H1 in a benchmark model containing almost mass-degenerate gluinos and light-flavour squarks. Under the assumption of an SM-like branching fraction, H1 bosons with masses in the range 40-120GeV arising from the decays of squarks or gluinos with a mass of 1200-2500GeV are excluded at 95% confidence level.
          Cover page: Search for light Higgs bosons from supersymmetric cascade decays in pp collisions at s=13TeV.
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2023)
          A search for decays to invisible particles of Higgs bosons produced in association with a top-antitop quark pair or a vector boson, which both decay to a fully hadronic final state, has been performed using proton-proton collision data collected at s=13TeV by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138fb-1. The 95% confidence level upper limit set on the branching fraction of the 125GeV Higgs boson to invisible particles, B(H→inv), is 0.54 (0.39 expected), assuming standard model production cross sections. The results of this analysis are combined with previous B(H→inv) searches carried out at s=7, 8, and 13TeV in complementary production modes. The combined upper limit at 95% confidence level on B(H→inv) is 0.15 (0.08 expected).
            Cover page: A search for decays of the Higgs boson to invisible particles in events with a top-antitop quark pair or a vector boson in proton-proton collisions at s=13TeV
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2021)
            Production cross sections of the Higgs boson are measured in the H→ZZ→4ℓ ( ℓ=e,μ ) decay channel. A data sample of proton-proton collisions at a center-of-mass energy of 13 TeV , collected by the CMS detector at the LHC and corresponding to an integrated luminosity of 137 fb-1 is used. The signal strength modifier μ , defined as the ratio of the Higgs boson production rate in the 4ℓ channel to the standard model (SM) expectation, is measured to be μ=0.94±0.07(stat)-0.08+0.09(syst) at a fixed value of mH=125.38GeV . The signal strength modifiers for the individual Higgs boson production modes are also reported. The inclusive fiducial cross section for the H→4ℓ process is measured to be 2.84-0.22+0.23(stat)-0.21+0.26(syst)fb , which is compatible with the SM prediction of 2.84±0.15fb for the same fiducial region. Differential cross sections as a function of the transverse momentum and rapidity of the Higgs boson, the number of associated jets, and the transverse momentum of the leading associated jet are measured. A new set of cross section measurements in mutually exclusive categories targeted to identify production mechanisms and kinematical features of the events is presented. The results are in agreement with the SM predictions.
              Cover page: Measurements of production cross sections of the Higgs boson in the four-lepton final state in proton-proton collisions at s=13TeV.
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2021)
              A combination of searches for top squark pair production using proton-proton collision data at a center-of-mass energy of 13 Te at the CERN LHC, corresponding to an integrated luminosity of 137 fb-1 collected by the CMS experiment, is presented. Signatures with at least 2 jets and large missing transverse momentum are categorized into events with 0, 1, or 2 leptons. New results for regions of parameter space where the kinematical properties of top squark pair production and top quark pair production are very similar are presented. Depending on the model, the combined result excludes a top squark mass up to 1325 Ge for a massless neutralino, and a neutralino mass up to 700 Ge for a top squark mass of 1150 Ge . Top squarks with masses from 145 to 295 Ge , for neutralino masses from 0 to 100 Ge , with a mass difference between the top squark and the neutralino in a window of 30 Ge around the mass of the top quark, are excluded for the first time with CMS data. The results of theses searches are also interpreted in an alternative signal model of dark matter production via a spin-0 mediator in association with a top quark pair. Upper limits are set on the cross section for mediator particle masses of up to 420 Ge .
                Cover page: Combined searches for the production of supersymmetric top quark partners in proton-proton collisions at s=13Te.
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2024)
                A search for exotic decays of the Higgs boson (H) with a mass of 125GeV to a pair of light pseudoscalars a1 is performed in final states where one pseudoscalar decays to two b quarks and the other to a pair of muons or τ leptons. A data sample of proton-proton collisions at s=13TeV corresponding to an integrated luminosity of 138fb-1 recorded with the CMS detector is analyzed. No statistically significant excess is observed over the standard model backgrounds. Upper limits are set at 95% confidence level (CL) on the Higgs boson branching fraction to μμbb and to ττbb, via a pair of a1s. The limits depend on the pseudoscalar mass ma1 and are observed to be in the range (0.17-3.3) ×10-4 and (1.7-7.7) ×10-2 in the μμbb and ττbb final states, respectively. In the framework of models with two Higgs doublets and a complex scalar singlet (2HDM+S), the results of the two final states are combined to determine upper limits on the branching fraction B(H→a1a1→ℓℓbb) at 95% CL, with ℓ being a muon or a τ lepton. For different types of 2HDM+S, upper bounds on the branching fraction B(H→a1a1) are extracted from the combination of the two channels. In most of the Type II 2HDM+S parameter space, B(H→a1a1) values above 0.23 are excluded at 95% CL for ma1 values between 15 and 60GeV.
                  Cover page: Search for exotic decays of the Higgs boson to a pair of pseudoscalars in the μμbb and ττbb final states.
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2021)
                  The production of Z boson pairs in proton-proton ( pp ) collisions, pp→(Z/γ∗)(Z/γ∗)→2ℓ2ℓ' , where ℓ,ℓ'=e or μ , is studied at a center-of-mass energy of 13 TeV with the CMS detector at the CERN LHC. The data sample corresponds to an integrated luminosity of 137 fb-1 , collected during 2016-2018. The ZZ production cross section, σtot(pp→ZZ)=17.4±0.3(stat)±0.5(syst)±0.4(theo)±0.3(lumi) pb , measured for events with two pairs of opposite-sign, same-flavor leptons produced in the mass region 60
                    Cover page: Measurements of pp→ZZ production cross sections and constraints on anomalous triple gauge couplings at s=13TeV
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2022)
                    Measurements of the associated production of a W boson and a charm ( c ) quark in proton-proton collisions at a centre-of-mass energy of 8 TeV are reported. The analysis uses a data sample corresponding to a total integrated luminosity of 19.7 fb-1 collected by the CMS detector at the LHC. The W bosons are identified through their leptonic decays to an electron or a muon, and a neutrino. Charm quark jets are selected using distinctive signatures of charm hadron decays. The product of the cross section and branching fraction σ(pp→W+c+X)B(W→ℓν) , where ℓ=e or μ , and the cross section ratio σ(pp→W++c¯+X)/σ(pp→W-+c+X) are measured in a fiducial volume and differentially as functions of the pseudorapidity and of the transverse momentum of the lepton from the W boson decay. The results are compared with theoretical predictions. The impact of these measurements on the determination of the strange quark distribution is assessed.
                      Cover page: Measurements of the associated production of a W boson and a charm quark in proton-proton collisions at s=8TeV.
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