613 research outputs found

    Search for WÂŽ bosons decaying to a top and a bottom quark at root s=13 TeV in the hadronic final state

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    A search is performed for W ' bosons decaying to a top and a bottom quark in the all-hadronic final state, in proton-proton collisions at a center-of-mass energy of 13TeV. The analyzed data were collected by the CMS experiment between 2016 and 2018 and correspond to an integrated luminosity of 137fb(-1). Deep neural network algorithms are used to identify the jet initiated by the bottom quark and the jet containing the decay products of the top quark when the W ' boson from the top quark decays hadronically. No excess above the estimated standard model background is observed. Upper limits on the production cross sections of W ' bosons decaying to a top and a bottom quark are set. Both left- and right-handed W ' bosons with masses below 3.4TeV are excluded at 95% confidence level, and the most stringent limits to date on W ' bosons decaying to a top and a bottom quark in the all-hadronic final state are obtained. (C) 2021 The Author(s). Published by Elsevier B.V.Peer reviewe

    Study of dijet events with large rapidity separation in proton-proton collisions at s \sqrt{s} = 2.76 TeV

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    The cross sections for inclusive and Mueller-Navelet dijet production are measured as a function of the rapidity separation between the jets in proton-proton collisions at s√ = 2.76 TeV for jets with transverse momentum pT > 35 GeV and rapidity |y| 20 GeV is introduced to improve the sensitivity to the effects of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution. The measurement is compared with the predictions of various Monte Carlo models based on leading-order and next-to-leading-order calculations including the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi leading-logarithm (LL) parton shower as well as the LL BFKL resummation

    Measurement of the top quark mass using events with a single reconstructed top quark in pp collisions at s\sqrt{s} = 13 TeV

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    A measurement of the top quark mass is performed using a data sample enriched with single top quark events produced in the t channel. The study is based on proton- proton collision data, corresponding to an integrated luminosity of 35.9 fb−1^{-1}, recorded at s\sqrt{s} = 13 TeV by the CMS experiment at the LHC in 2016. Candidate events are selected by requiring an isolated high-momentum lepton (muon or electron) and exactly two jets, of which one is identified as originating from a bottom quark. Multivariate discriminants are designed to separate the signal from the background. Optimized thresholds are placed on the discriminant outputs to obtain an event sample with high signal purity. The top quark mass is found to be 172.13+0.76^{+0.76}−0.77_{-0.77} GeV, where the uncertainty includes both the statistical and systematic components, reaching sub-GeV precision for the first time in this event topology. The masses of the top quark and antiquark are also determined separately using the lepton charge in the final state, from which the mass ratio and difference are determined to be 0.9952+0.0079^{+0.0079}−0.0104_{-0.0104} and 0.83+1.79^{+1.79}−1.35_{-1.35} GeV, respectively. The results are consistent with CPT invariance

    Search for flavor-changing neutral current interactions of the top quark and the Higgs boson decaying to a bottom quark-antiquark pair at s√ = 13 TeV

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    A search for flavor-changing neutral current interactions of the top quark (t) and the Higgs boson (H) is presented. The search is based on a data sample corresponding to an integrated luminosity of 137 fb−1 recorded by the CMS experiment at the LHC in proton-proton collisions at s√ = 13 TeV. Events containing exactly one lepton (muon or electron) and at least three jets, among which at least two are identified as originating from the hadronization of a bottom quark, are analyzed. A set of deep neural networks is used for kinematic event reconstruction, while boosted decision trees distinguish the signal from the background events. No significant excess over the background predictions is observed, and upper limits on the signal production cross sections are extracted. These limits are interpreted in terms of top quark decay branching fractions (B ) to the Higgs boson and an up (u) or a charm quark (c). Assuming one nonvanishing extra coupling at a time, the observed (expected) upper limits at 95% confidence level are B (t → Hu) < 0.079 (0.11)% and B (t → Hc) < 0.094 (0.086)%

    Search for a vector-like quark Tâ€Č → tH via the diphoton decay mode of the Higgs boson in proton-proton collisions at s \sqrt{s} = 13 TeV

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    A search for the electroweak production of a vector-like quark Tâ€Č, decaying to a top quark and a Higgs boson is presented. The search is based on a sample of proton-proton collision events recorded at the LHC at = 13 TeV, corresponding to an integrated luminosity of 138 fb−1. This is the first Tâ€Č search that exploits the Higgs boson decay to a pair of photons. For narrow isospin singlet Tâ€Č states with masses up to 1.1 TeV, the excellent diphoton invariant mass resolution of 1–2% results in an increased sensitivity compared to previous searches based on the same production mechanism. The electroweak production of a Tâ€Č quark with mass up to 960 GeV is excluded at 95% confidence level, assuming a coupling strength ÎșT = 0.25 and a relative decay width Γ/MTâ€Č < 5%

    Search for heavy resonances decaying to Z(ΜΜˉ\bar{Îœ}) V(qqˉ\bar{q}â€Č) in proton-proton collisions at √s = 13 TeV

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    Search for new particles in an extended Higgs sector with four b quarks in the final state at √s = 13 TeV

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    Search for invisible decays of the Higgs boson produced via vector boson fusion in proton-proton collisions at s\sqrt{s} = 13 TeV

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    A search for invisible decays of the Higgs boson produced via vector boson fusion (VBF) has been performed with 101  fb−1^{-1} of proton-proton collisions delivered by the LHC at s\sqrt{s} =13  TeV and collected by the CMS detector in 2017 and 2018. The sensitivity to the VBF production mechanism is enhanced by constructing two analysis categories, one based on missing transverse momentum and a second based on the properties of jets. In addition to control regions with Z and W boson candidate events, a highly populated control region, based on the production of a photon in association with jets, is used to constrain the dominant irreducible background from the invisible decay of a Z boson produced in association with jets. The results of this search are combined with all previous measurements in the VBF topology, based on data collected in 2012 (at s\sqrt{s} =8  TeV), 2015, and 2016, corresponding to integrated luminosities of 19.7, 2.3, and 36.3  fb−1^{-1}, respectively. The observed (expected) upper limit on the invisible branching fraction of the Higgs boson is found to be 0.18 (0.10) at the 95% confidence level, assuming the standard model production cross section. The results are also interpreted in the context of Higgs-portal models

    Observation of the Bc+_\mathrm{c}^+ Meson in Pb-Pb and pp Collisions at sNN\sqrt{s_{\mathrm{NN}}} = 5.02 TeV and Measurement of its Nuclear Modification Factor

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    The Bc+_\mathrm{c}^+ meson is observed for the first time in heavy ion collisions. Data from the CMS detector are used to study the production of the Bc+_\mathrm{c}^+ meson in lead-lead (Pb-Pb) and proton-proton (pp) collisions at a center-of-mass energy per nucleon pair of sNN\sqrt{s_{\mathrm{NN}}} = 5.02 TeV , via the Bc+_\mathrm{c}^+ → (J/ψ → ÎŒ+^+Ό−^−)ÎŒ+^+ΜΌ_ÎŒ decay. The Bc+_\mathrm{c}^+ nuclear modification factor, derived from the PbPb-to-pp ratio of production cross sections, is measured in two bins of the trimuon transverse momentum and of the PbPb collision centrality. The Bc+_\mathrm{c}^+meson is shown to be less suppressed than quarkonia and most of the open heavy-flavor mesons, suggesting that effects of the hot and dense nuclear matter created in heavy ion collisions contribute to its production. This measurement sets forth a promising new probe of the interplay of suppression and enhancement mechanisms in the production of heavy-flavor mesons in the quark-gluon plasma

    Measurements of Higgs boson production cross sections and couplings in the diphoton decay channel at s \sqrt{\mathrm{s}} = 13 TeV

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    Measurements of Higgs boson production cross sections and couplings in events where the Higgs boson decays into a pair of photons are reported. Events are selected from a sample of proton-proton collisions at s √ s = 13 TeV collected by the CMS detector at the LHC from 2016 to 2018, corresponding to an integrated luminosity of 137 fb−1. Analysis categories enriched in Higgs boson events produced via gluon fusion, vector boson fusion, vector boson associated production, and production associated with top quarks are constructed. The total Higgs boson signal strength, relative to the standard model (SM) prediction, is measured to be 1.12±0.09. Other properties of the Higgs boson are measured, including SM signal strength modifiers, production cross sections, and its couplings to other particles. These include the most precise measurements of gluon fusion and vector boson fusion Higgs boson production in several different kinematic regions, the first measurement of Higgs boson production in association with a top quark pair in five regions of the Higgs boson transverse momentum, and an upper limit on the rate of Higgs boson production in association with a single top quark. All results are found to be in agreement with the SM expectations
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