42 research outputs found

    Electron and photon reconstruction and identification with the CMS experiment at the CERN LHC

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    The performance is presented of the reconstruction and identification algorithms for electrons and photons with the CMS experiment at the LHC. The reported results are based on proton-proton collision data collected at a center-of-mass energy of 13 TeV and recorded in 2016-2018, corresponding to an integrated luminosity of 136 fb(-1). Results obtained from lead-lead collision data collected at root S-NN = 5.02 TeV are also presented. Innovative techniques are used to reconstruct the electron and photon signals in the detector and to optimize the energy resolution. Events with electrons and photons in the final state are used to measure the energy resolution and energy scale uncertainty in the recorded events. The measured energy resolution for electrons produced in Z boson decays in proton-proton collision data ranges from 2 to 5%, depending on electron pseudorapidity and energy loss through bremsstrahlung in the detector material. The energy scale in the same range of energies is measured with an uncertainty smaller than 0.1 (0.3)% in the barrel (endcap) region in proton-proton collisions and better than 1(3)% in the barrel (endcap) region in heavy ion collisions. The timing resolution for electrons from Z boson decays with the full 2016-2018 proton-proton collision data set is measured to be 200 ps.Peer reviewe

    Nuclear modification of Y states in pPb collisions at √SNN_{NN} = 5.02 TeV

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    Production cross sections of Υ(1S), Υ(2S), and Υ(3S) states decaying into μ+μ− in proton-lead (pPb) collisions are reported using data collected by the CMS experiment at √sNN = 5.02 TeV. A comparison is made with corresponding cross sections obtained with pp data measured at the same collision energy and scaled by the Pb nucleus mass number. The nuclear modification factor for Υ(1S) is found to be RpPb(Υ(1S)) = 0.806±0.024 (stat)±0.059 (syst). Similar results for the excited states indicate a sequential suppression pattern, such that RpPb(Υ(1S)) > RpPb(Υ(2S)) > RpPb(Υ(3S)). The suppression of all states is much less pronounced in pPb than in PbPb collisions, and independent of transverse momentum pΥT and center-of-mass rapidity yΥCM of the individual Υ state in the studied range p ΥT < 30 GeV/c and |yΥCM| <1.93. Models that incorporate final-state effects of bottomonia in pPb collisions are in better agreement with the data than those which only assume initial-state modifications

    Search for resonant pair production of Higgs bosons in the bbZZ channel in proton-proton collisions at root s=13 TeV

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    A search for the production of a narrow-width resonance decaying into a pair of Higgs bosons decaying into the bbZZ channel is presented. The analysis is based on data collected with the CMS detector during 2016, in proton-proton collisions at the LHC, corresponding to an integrated luminosity of 35.9 fb(-1). The final states considered are the ones where one of the Z bosons decays into a pair of muons or electrons, and the other Z boson decays to either a pair of quarks or a pair of neutrinos. Upper limits at 95% confidence level are placed on the production of narrow-width spin-0 or spin-2 particles decaying to a pair of Higgs bosons, in models with and without an extended Higgs sector. For a resonance mass range between 260 and 1000 GeV, limits on the production cross section times branching fraction of a spin-0 and spin-2 resonance range from 0.1 to 5.0 pb and 0.1 to 3.6 pb, respectively. These results set limits in parameter space in bulk Randall-Sundrum radion, Kaluza-Klein excitation of the graviton, and next-to-minimal two-Higgs doublet models (N2HDMs). For specific choices of parameters the N2HDM can be excluded in a mass range between 360 and 620 GeV for a resonance decaying to two Higgs bosons. This is the first search for Higgs boson resonant pair production in the bbZZ channel.Peer reviewe

    Using Z boson events to study parton-medium interactions in Pb-Pb collisions

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    The spectra measurements of charged hadrons produced in the shower of a parton originating in the same hard scattering with a leptonically decaying Z boson are reported in lead-lead nuclei (Pb-Pb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Both Pb-Pb and pp data sets are recorded by the CMS experiment at the LHC and correspond to an integrated luminosity of 1.7  nb^{-1} and 320  pb^{-1}, respectively. Hadronic collision data with one reconstructed Z boson candidate with the transverse momentum p_{T}>30  GeV/c are analyzed. The Z boson constrains the initial energy and direction of the associated parton. In heavy ion events, azimuthal angular distributions of charged hadrons with respect to the direction of a Z boson are sensitive to modifications of the in-medium parton shower and medium response. compared to reference data from pp interactions, the results for central Pb-Pb collisions indicate a modification of the angular correlations. The measurements of the fragmentation functions and p_{T} spectra of charged particles in Z boson events, which are sensitive to medium modifications of the parton shower longitudinal structure, are also reported. Significant modifications in central Pb-Pb events compared to the pp reference data are also found for these observables

    Nuclear modification of Y states in pPb collisions at √sNN = 5.02 TeV

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    Production cross sections of Υ(1S), Υ(2S), and Υ(3S) states decaying into μ+μ− in proton-lead (pPb) collisions are reported using data collected by the CMS experiment at √sNN = 5.02 TeV. A comparison is made with corresponding cross sections obtained with pp data measured at the same collision energy and scaled by the Pb nucleus mass number. The nuclear modification factor for Υ(1S) is found to be RpPb(Υ(1S)) = 0.806±0.024 (stat)±0.059 (syst). Similar results for the excited states indicate a sequential suppression pattern, such that RpPb(Υ(1S)) > RpPb(Υ(2S)) > RpPb(Υ(3S)). The suppression of all states is much less pronounced in pPb than in PbPb collisions, and independent of transverse momentum p Υ T and center-of-mass rapidity y Υ CM of the individual Υ state in the studied range p Υ T < 30 GeV/c and |y Υ CM| < 1.93. Models that incorporate final-state effects of bottomonia in pPb collisions are in better agreement with the data than those which only assume initial-state modifications

    Search for strongly interacting massive particles generating trackless jets in proton–proton collisions at s√ = 13 TeV

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    Data Availability Statement: This manuscript has no associated data or the data will not be deposited. [Authors’ comment: Release and preservation of data used by the CMS Collaboration as the basis for publications is guided by the CMS policy as stated in “CMS data preservation, re-use and open access policy” (https://cms-docdb.cern.ch/cgi-bin/ PublicDocDB/RetrieveFile?docid=6032&filename=CMSDataPolicyV1. 2.pdf&version=2).]Copyright © 2022 The Authors. A search for dark matter in the form of strongly interacting massive particles (SIMPs) using the CMS detector at the LHC is presented. The SIMPs would be produced in pairs that manifest themselves as pairs of jets without tracks. The energy fraction of jets carried by charged particles is used as a key discriminator to suppress efficiently the large multijet background, and the remaining background is estimated directly from data. The search is performed using proton–proton collision data corresponding to an integrated luminosity of 16.1fb−1, collected with the CMS detector in 2016. No significant excess of events is observed above the expected background. For the simplified dark matter model under consideration, SIMPs with masses up to 100GeV are excluded and further sensitivity is explored towards higher masses.SCOAP3

    Performance of the CMS muon trigger system in proton-proton collisions at root s=13 TeV

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    The muon trigger system of the CMS experiment uses a combination of hardware and software to identify events containing a muon. During Run 2 (covering 2015–2018) the LHC achieved instantaneous luminosities as high as 2 × 1034 while delivering proton-proton collisions at √(s) = 13. The challenge for the trigger system of the CMS experiment is to reduce the registered event rate from about 40MHz to about 1kHz. Significant improvements important for the success of the CMS physics program have been made to the muon trigger system via improved muon reconstruction and identification algorithms since the end of Run 1 and throughout the Run 2 data-taking period. The new algorithms maintain the acceptance of the muon triggers at the same or even lower rate throughout the data-taking period despite the increasing number of additional proton-proton interactions in each LHC bunch crossing. In this paper, the algorithms used in 2015 and 2016 and their improvements throughout 2017 and 2018 are described. Measurements of the CMS muon trigger performance for this data-taking period are presented, including efficiencies, transverse momentum resolution, trigger rates, and the purity of the selected muon sample. This paper focuses on the single- and double-muon triggers with the lowest sustainable transverse momentum thresholds used by CMS. The efficiency is measured in a transverse momentum range from 8 to several hundred

    Search for CP violating top quark couplings in pp collisions at 1as=13 TeV

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    Abstract: Results are presented from a search for CP violation in top quark pair production, using proton-proton collisions at a center-of-mass energy of 13TeV. The data used for this analysis consist of final states with two charged leptons collected by the CMS experiment, and correspond to an integrated luminosity of 35.9 fb(-1). The search uses two observables, O-1 and O-3, which are Lorentz scalars. The observable O-1 is constructed from the four-momenta of the charged leptons and the reconstructed top quarks, while O-3 consists of the four-momenta of the charged leptons and the b quarks originating from the top quarks. Asymmetries in these observables are sensitive to CP violation, and their measurement is used to determine the chromoelectric dipole moment of the top quark. The results are consistent with the expectation from the standard model

    Performance of the CMS muon trigger system in proton-proton collisions at 1as=13 TeV

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    Observation of same-sign WW production from double parton scattering in proton-proton collisions at 1as=13 TeV

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    Abstract: The first observation of the production of (WW +/-)-W-+/- bosons from double parton scattering processes using same-sign electron-muon and dimuon events in proton-proton collisions is reported. The data sample corresponds to an integrated luminosity of 138 fb(-1 )recorded at a center-of-mass energy of 13 TeV using the CMS detector at the CERN LHC. Multivariate discriminants are used to distinguish the signal process from the main backgrounds. A binned maximum likelihood fit is performed to extract the signal cross section. The measured cross section for production of same-sign W bosons decaying leptonically is 80.7 +/- 11.2(stat)( -8.6)(+9.5)(syst) +/- 12.1(model) fb, whereas the measured fiducial cross section is 6.28 +/- 0.81(stat) +/- 0.69(syst) +/- 0.37(model) fb. The observed significance of the signal is 6.2 standard deviations above the background-only hypothesis
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