107 Search Results

A search for the production of a top quark in association with a photon and additional jets via flavor changing neutral current interactions is presented. The analysis uses proton-proton collision data recorded by the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb^-1. The search is performed by looking for processes where a single top quark is produced in association with a photon, or a pair of top quarks where one of the top quarks decays into a photon and an up or charm quark. Events with an electron or a muon,more » a photon, one or more jets, and missing transverse momentum are selected. Multivariate analysis techniques are used to discriminate signal and standard model background processes. No significant deviation is observed over the predicted background. Observed (expected) upper limits are set on the branching fractions of top quark decays:$$\mathscr{B}$$(t → uγ)< 0.95 × 10^-5 (1.20 × 10^-5) and $$\mathscr{B}$$(t → cγ) < 1.51 × 10^-5 (1.54 × 10^-5) at 95% confidence level, assuming a single nonzero coupling at a time. The obtained limit for $$\mathscr{B}$$(t → uγ) is similar to the current best limit, while the limit for $$\mathscr{B}$$(t→ cγ) is significantly tighter than previous results.« less

The observation of WW$$\gamma$$ production in proton-proton collisions at a center-of-mass energy of 13 TeV with an integrated luminosity of 138 fb^-1 is presented. The observed (expected) significance is 5.6 (5.1) standard deviations. Events are selected by requiring exactly two leptons (one electron and one muon) of opposite charge, moderate missing transverse momentum, and a photon. The measured fiducial cross section for WW$$\gamma$$ is 5.9 ± 0.8 (stat) ± 0.8 (syst) ± 0.7 (modeling) fb, in agreement with the next-to-leading order quantum chromodynamics prediction. The analysis is extended with a search for the associated production of the Higgs boson andmore » a photon, which is generated by a coupling of the Higgs boson to light quarks. The result is used to constrain the Higgs boson couplings to light quarks.« less

A search for an exotic decay of the Higgs boson to a Z boson and a light pseudoscalar particle (a), decaying to a pair of leptons and a pair of photons, respectively, is presented. The search is based on proton-proton collision data at a center-of-mass energy of $$\sqrt{s}$$ = 13 TeV, collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 138 fb^-1. The analysis probes pseudoscalar masses m_a between 1 and 30 GeV, leading to two pairs of well-isolated leptons and photons. Upper limits at 95% confidence level are set on the Higgs bosonmore » production cross section times its branching fraction to two leptons and two photons. The observed (expected) limits are in the range of 1.1–17.8 (1.7–17.9) fb within the probed m_a interval. An excess of data above the expected standard model background with a local (global) significance of 2.6 (1.3) standard deviations is observed for a mass hypothesis of m_a = 3GeV. Limits on models involving axion-like particles, formulated as an effective field theory, are also reported.« less

A search is reported for near-threshold structures in the J/ψJ/ψ invariant mass spectrum produced in proton-proton collisions at $$\sqrt{s}$$ =13 TeV from data collected by the CMS experiment, corresponding to an integrated luminosity of 135 fb^-1. Three structures are found, and a model with quantum interference among these structures provides a good description of the data. A new structure is observed with a local significance above 5 standard deviations at a mass of 6638$$^{+43}_{-38}$$(stat)$$^{+16}_{-31}$$ (syst) MeV. Another structure with even higher significance is found at a mass of 6847$$^{+44}_{-28}$$(stat)$$^{+48}_{-20}$$(syst) MeV, which is consistent with the X(6900) resonance reported by themore » LHCb experiment and confirmed by the ATLAS experiment. Evidence for another new structure, with a local significance of 4.7 standard deviations, is found at a mass of 7134$$^{+48}_{-25}$$(stat) $$^{+41}_{-15}$$(syst) MeV. Results are also reported for a model without interference, which does not fit the data as well and shows mass shifts up to 150 MeV relative to the model with interference.« less

The azimuthal anisotropy of Image 1 mesons in high-multiplicity proton-lead collisions is studied using data collected by the CMS experiment at a nucleon-nucleon center-of-mass energy of 8.16 TeV. The Image 1 mesons are reconstructed using their dimuon decay channel. The anisotropy is characterized by the second Fourier harmonic coefficients, found using a two-particle correlation technique, in which the Image 1 mesons are correlated with charged hadrons. A large pseudorapidity gap is used to suppress short-range correlations. Nonflow contamination from the dijet background is removed using a low-multiplicity subtraction method, and the results are presented as a function of Image 1more » transverse momentum. The azimuthal anisotropies are smaller than those found for charmonia in proton-lead collisions at the same collision energy, but are consistent with values found for Image 1 mesons in lead-lead interactions at a nucleon-nucleon center-of-mass energy of 5.02 TeV.« less

The identification of prompt and isolated muons, as well as muons from heavy-flavour hadron decays, is an important task. We developed two multivariate techniques to provide highly efficient identification for muons with transverse momentum greater than 10 GeV. One provides a continuous variable as an alternative to a cut-based identification selection and offers a better discrimination power against misidentified muons. The other one selects prompt and isolated muons by using isolation requirements to reduce the contamination from nonprompt muons arising in heavy-flavour hadron decays. Both algorithms are developed using 59.7 fb^-1 of proton-proton collisions data at a centre-of-mass energy ofmore » $$\sqrt{(s)}$$=13 TeV collected in 2018 with the CMS experiment at the CERN LHC.« less

Two-particle Bose–Einstein momentum correlation functions are studied for charged-hadron pairs in lead-lead collisions at a center-of-mass energy per nucleon pair of $$\sqrt{s_{NN}}$$ = 5.02 TeV. The data sample, containing 4.27 × 10⁹ minimum bias events corresponding to an integrated luminosity of 0.607 nb^-1, was collected by the CMS experiment in 2018. The experimental results are discussed in terms of a Lévy-type source distribution. The parameters of this distribution are extracted as functions of particle pair average transverse mass and collision centrality. These parameters include the Lévy index or shape parameter α, the Lévy scale parameter R, and the correlation strengthmore » parameter λ. The source shape, characterized by α, is found to be neither Cauchy nor Gaussian, implying the need for a full Lévy analysis. Similarly to what was previously found for systems characterized by Gaussian source radii, a hydrodynamical scaling is observed for the Lévy R parameter. The λ parameter is studied in terms of the core-halo model.« less

Measurements of the elliptic ($$v$$₂) and triangular ($$v$$₃) azimuthal anisotropy coefficients are presented for D⁰ mesons produced in b hadron decays (nonprompt D⁰ mesons) in lead-lead collisions at $$\sqrt{s_{NN}}$$ = 5.02 TeV. The results are compared with previously published charm meson anisotropies measured using prompt D⁰ mesons. The data were collected with the CMS detector in 2018 with an integrated luminosity of 0.58 nb^–1. Azimuthal anisotropy is sensitive to the interactions of quarks with the hot and dense medium created in heavy ion collisions. Comparing results for prompt and nonprompt D⁰ mesons can assist in understanding the mass dependence ofmore » these interactions. The nonprompt results show lower magnitudes of $$v$$₂ and $$v$$₃ and weaker dependences on the meson transverse momentum and collision centrality than those found for prompt D⁰ mesons. The results are in agreement with theoretical predictions that include a mass dependence in the interactions of quarks with the medium« less

The first search for scalar leptoquarks produced in τ-lepton–quark collisions is presented. It is based on a set of proton-proton collision data recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb^–1. The reconstructed final state consists of a jet, significant missing transverse momentum, and a τ lepton reconstructed through its hadronic or leptonic decays. Limits are set on the product of the leptoquark production cross section and branching fraction and interpreted as exclusions in the plane of the leptoquark mass and the leptoquark-τ-quark coupling strength.

A search is presented for new Higgs bosons in proton-proton (pp) collision events in which a same-sign top quark pair is produced in association with a jet, via the pp $$\to$$ tH/A $$\to$$ tt$$\mathrm{\bar{c}}$$ and pp $$\to$$ tH/A $$\to$$ tt$$\mathrm{\bar{u}}$$ processes. Here, H and A represent the extra scalar and pseudoscalar boson, respectively, of the second Higgs doublet in the generalized two-Higgs-doublet model (g2HDM). The search is based on pp collision data collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb$$^{-1}$$. Final states with a same-signmore » lepton pair in association with jets and missing transverse momentum are considered. New Higgs bosons in the 200-1000 GeV mass range and new Yukawa couplings between 0.1 and 1.0 are targeted in the search, for scenarios in which either H or A appear alone, or in which they coexist and interfere. No significant excess above the standard model prediction is observed. Exclusion limits are derived in the context of the g2HDM.« less