A search for beyond the standard model spin-0 bosons, ϕ, that decay into pairs of electrons, muons, or tau leptons is presented. The search targets the associated production of such bosons with a W or Z gauge boson, o...
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A search for beyond the standard model spin-0 bosons, ϕ, that decay into pairs of electrons, muons, or tau leptons is presented. The search targets the associated production of such bosons with a W or Z gauge boson, or a top quark-antiquark pair, and uses events with three or four charged leptons, including hadronically decaying tau leptons. The proton-proton collision data set used in the analysis was collected at the LHC from 2016 to 2018 at a center-of-mass energy of 13 TeV, and corresponds to an integrated luminosity of 138 fb−1. The observations are consistent with the predictions from standard model processes. Upper limits are placed on the product of cross sections and branching fractions of such new particles over the mass range of 15 to 350 GeV with scalar, pseudoscalar, or Higgs-boson-like couplings, as well as on the product of coupling parameters and branching fractions. Several model-dependent exclusion limits are also presented. For a Higgs-boson-like ϕ model, limits are set on the mixing angle of the Higgs boson with the ϕ boson. For the associated production of a ϕ boson with a top quark-antiquark pair, limits are set on the coupling to top quarks. Finally, limits are set for the first time on a fermiophilic dilaton-like model with scalar couplings and a fermiophilic axion-like model with pseudoscalar couplings.
The first observation of the decay Ξb−→ψ(2S)Ξ− and measurement of the branching ratio of Ξb−→ψ(2S)Ξ− to Ξb−→J/ψΞ− are presented. The J/ψ and ψ(2S) mesons are reconstructed using their dimuon decay modes....
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The first observation of the decay Ξb−→ψ(2S)Ξ− and measurement of the branching ratio of Ξb−→ψ(2S)Ξ− to Ξb−→J/ψΞ− are presented. The J/ψ and ψ(2S) mesons are reconstructed using their dimuon decay modes. The results are based on proton-proton colliding beam data from the LHC collected by the CMS experiment at s=13 TeV in 2016–2018, corresponding to an integrated luminosity of 140 fb−1. The branching fraction ratio is measured to be b(Ξb−→ψ(2S)Ξ−)/b(Ξb−→J/ψΞ−)=0.84−0.19+0.21(stat)±0.10(syst)±0.02(b), where the last uncertainty comes from the uncertainties in the branching fractions of the charmonium states. New measurements of the Ξb(5945)0 baryon mass and natural width are also presented, using the Ξb−π+ final state, where the Ξb− baryon is reconstructed through the decays J/ψΞ−, ψ(2S)Ξ−, J/ψΛK−, and J/ψΣ0K−. Finally, the fraction of Ξb− baryons produced from Ξb(5945)0 decays is determined.
A search for heavy neutral leptons (HNLs) decaying in the CMS muon system is presented. A data sample is used corresponding to an integrated luminosity of 138 fb−1 of proton-proton collisions at s=13 TeV, recorded a...
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A search for heavy neutral leptons (HNLs) decaying in the CMS muon system is presented. A data sample is used corresponding to an integrated luminosity of 138 fb−1 of proton-proton collisions at s=13 TeV, recorded at the CERN LHC in 2016–2018. Decay products of long-lived HNLs could interact with the shielding materials in the CMS muon system and create hadronic and electromagnetic showers detected in the muon chambers. This distinctive signature provides a unique handle to search for HNLs with masses below 4 GeV and proper decay lengths of the order of meters. The signature is sensitive to HNL couplings to all three generations of leptons. Candidate events are required to contain a prompt electron or muon originating from a vertex on the beam axis and a displaced shower in the muon chambers. No significant deviations from the standard model background expectation are observed. In the electron (muon) channel, the most stringent limits to date are set for HNLs in the mass range of 2.1–3.0 (1.9–3.3) GeV, reaching mixing matrix element squared values as low as 8.6(4.6)×10−6.
The J/ψ→μ+μ−μ+μ− decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of ...
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The J/ψ→μ+μ−μ+μ− decay has been observed with a statistical significance in excess of five standard deviations. The analysis is based on an event sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment in 2018 and corresponding to an integrated luminosity of 33.6 fb−1. Normalizing to the J/ψ→μ+μ− decay mode leads to a branching fraction of [10.1−2.7+3.3(stat)±0.4(syst)]×10−7, a value that is consistent with the standard model prediction.
A search for the production of long-lived particles in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC is presented. The search is based on data collected by the CMS experiment in 2016–2...
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A search for the production of long-lived particles in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC is presented. The search is based on data collected by the CMS experiment in 2016–2018, corresponding to a total integrated luminosity of 137 fb−1. This search is designed to be sensitive to long-lived particles with mean proper decay lengths between 0.1 and 1000 mm, whose decay products produce a final state with at least one displaced vertex and missing transverse momentum. A machine learning algorithm, which improves the background rejection power by more than an order of magnitude, is applied to improve the sensitivity. The observation is consistent with the standard model background prediction, and the results are used to constrain split supersymmetry (SUSY) and gauge-mediated SUSY breaking models with different gluino mean proper decay lengths and masses. This search is the first CMS search that shows sensitivity to hadronically decaying long-lived particles from signals with mass differences between the gluino and neutralino below 100 GeV. It sets the most stringent limits to date for split-SUSY models and gauge-mediated SUSY breaking models with gluino proper decay length less than 6 mm.
A search for electroweak production of a single vectorlike T quark in association with a bottom (b) quark in the all-hadronic decay channel is presented. This search uses proton-proton collision data at s=13 TeV coll...
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A search for electroweak production of a single vectorlike T quark in association with a bottom (b) quark in the all-hadronic decay channel is presented. This search uses proton-proton collision data at s=13 TeV collected by the CMS experiment at the CERN LHC during 2016–2018, corresponding to an integrated luminosity of 138 fb−1. The T quark is assumed to have charge 2/3 and decay to a top (t) quark and a Higgs (H) or Z boson. Hadronic decays of the t quark and the H or Z boson are reconstructed from the kinematic properties of jets, including those containing b hadrons. No deviation from the standard model prediction is observed in the reconstructed tH and tZ invariant mass distributions. The 95% confidence level upper limits on the product of the production cross section and branching fraction of a T quark produced in association with a b quark and decaying via tH or tZ range from 1260 to 68 fb for T quark masses of 600–1200 GeV.
The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resourc...
A search for nonresonant Higgs boson (H) pair production via gluon and vector boson (V) fusion is performed in the four-bottom-quark final state, using proton-proton collision data at 13 TeV corresponding to 138 fb−1...
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A search for nonresonant Higgs boson (H) pair production via gluon and vector boson (V) fusion is performed in the four-bottom-quark final state, using proton-proton collision data at 13 TeV corresponding to 138 fb−1 collected by the CMS experiment at the LHC. The analysis targets Lorentz-boosted H pairs identified using a graph neural network. It constrains the strengths relative to the standard model of the H self-coupling and the quartic VVHH couplings, κ2V, excluding κ2V=0 for the first time, with a significance of 6.3 standard deviations when other H couplings are fixed to their standard model values.
We present the first direct search for exotic Higgs boson decays H→AA, A→γγ in events with two photonlike objects. The hypothetical particle A is a low-mass spin-0 particle decaying promptly to a merged diphoton r...
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We present the first direct search for exotic Higgs boson decays H→AA, A→γγ in events with two photonlike objects. The hypothetical particle A is a low-mass spin-0 particle decaying promptly to a merged diphoton reconstructed as a single photonlike object. We analyze the data collected by the CMS experiment at s=13 TeV corresponding to an integrated luminosity of 136 fb−1. No excess above the estimated background is found. We set upper limits on the branching fraction b(H→AA→4γ) of (0.9–3.3)×10−3 at 95% confidence level for masses of A in the range 0.1–1.2 GeV.
We present an observation of photon-photon production of τ lepton pairs in ultraperipheral lead-lead collisions. The measurement is based on a data sample with an integrated luminosity of 404 μb−1 collected by the ...
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We present an observation of photon-photon production of τ lepton pairs in ultraperipheral lead-lead collisions. The measurement is based on a data sample with an integrated luminosity of 404 μb−1 collected by the CMS experiment at a center-of-mass energy per nucleon pair of sNN=5.02 TeV. The γγ→τ+τ− process is observed for τ+τ− events with a muon and three charged hadrons in the final state. The measured fiducial cross section is σ(γγ→τ+τ−)=4.8±0.6(stat)±0.5(syst) μb, where the second (third) term corresponds to the statistical (systematic) uncertainty in σ(γγ→τ+τ−) in agreement with leading-order QED predictions. Using σ(γγ→τ+τ−), we estimate a model-dependent value of the anomalous magnetic moment of the τ lepton of aτ=0.001−0.089+0.055.
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