101 Search Results

The results of a search for the production of two scalar bosons in final states with two photons and two tau leptons are presented. The search considers both nonresonant production of a Higgs boson pair, HH, and resonant production via a new boson X which decays either to HH or to H and a new scalar Y. The analysis uses up to 138 fb$$^{−1}$$ of proton-proton collision data, recorded between 2016 and 2018 by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV. No evidence for signal is found in the data. For the nonresonant production,more » the observed (expected) upper limit at 95% confidence level (CL) on the HH production cross section is set at 930 (740) fb, corresponding to 33 (26) times the standard model prediction. At 95% CL, HH production is observed (expected) to be excluded for values of κ$$_{λ}$$ outside the range between −12 (−9.4) and 17 (15). Observed (expected) upper limits at 95% CL for the X → HH cross section are found to be within 160 to 2200 (200 to 1800) fb, depending on the mass of X. In the X → Y(ττ)H(γγ) search, the observed (expected) upper limits on the product of the production cross section and decay branching fractions vary between 0.059–1.2 fb (0.087–0.68 fb). For the X → Y(γγ)H(ττ) search the observed (expected) upper limits on the product of the production cross section and Y → γγ branching fraction vary between 0.69–15 fb (0.73–8.3 fb) in the low Y mass search, tightening constraints on the next-to-minimal supersymmetric standard model, and between 0.64–10 fb (0.70–7.6 fb) in the high Y mass search.[graphic not available: see fulltext]« less

A pioneering machine-learning-based flavor-tagging algorithm combining same-side and opposite-side tagging is used to obtain the equivalent of 27$$\,$$000 tagged B$$^0_\mathrm{s}$$$$\to$$ J/$$\psi\, \phi$$(1020) decays from pp collisions at $$\sqrt{s} =$$ 13 TeV, collected by the CMS experiment and corresponding to an integrated luminosity of 96.5 fb$$^{-1}$$. A time- and flavor-dependent angular analysis of the $$\mu^+\mu^-$$K$$^+$$K$$^-$ final state is used to measure parameters of the $$\mathrm{B}^0_\mathrm{s}$$-$$\overline{\mathrm{B}}^0_\mathrm{s}$$ system. The weak phase is measured to be $$\phi_\mathrm{s}$$ = $$-$$73 $$\pm$$ 23 (stat) $$\pm$$ 7 (syst) mrad, which, combined with a $$\sqrt{s}$$ = 8 TeV CMS result, gives $$\phi_\mathrm{s}$$ = $$-$$74 $$\pm$$ 23 mrad. Thismore » value differs from zero by 3.2 standard deviations, providing evidence for $CP$ violation in B$$^0_\mathrm{s}$$$$\to$$ J/$$\psi\,\phi$$(1020) decays. All measured physics parameters are found to agree with standard model predictions where available.« less

A search for charged-lepton flavour violation (CLFV) in top quark (t) production and decay is presented. The search uses proton-proton collision data corresponding to 138 fb$$^{-1}$$ collected with the CMS experiment at $$\sqrt{s}$$ = 13 TeV. The signal consists of the production of a single top quark via a CLFV interaction or top quark pair production followed by a CLFV decay. The analysis selects events containing a hadronically decaying $$τ$$ lepton and a muon of opposite electric charge, as well as at least three jets, one of which is identified as originating from the fragmentation of a bottom quark. Machinemore » learning classification techniques are used to distinguish signal from standard model background events. The results of this search are consistent with the standard model expectations. The upper limits at 95% confidence level on the branching fraction $$\mathcal{B}$$ for CLFV top quark decays to a muon, a $$τ$$ lepton, and an up or a charm quark are set at $$\mathcal{B}$$(t $$\to$$ $μτ$u) $$\lt$$ (0.04, 0.08, and 0.12) $$\times$$ 10$$^{-6}$$, and $$\mathcal{B}$$(t $$\to$$ $μτ$c) $$\lt$$ (0.81, 1.71, and 2.05) $$\times$$ 10$$^{-6}$$ for scalar, vector, and tensor-like operators, respectively.« less

This paper presents a model-agnostic search for narrow resonances in the dijet final state in the mass range 1.8-6 TeV. The signal is assumed to produce jets with substructure atypical of jets initiated by light quarks or gluons, with minimal additional assumptions. Search regions are obtained by utilizing multivariate machine-learning methods to select jets with anomalous substructure. A collection of complementary anomaly detection methods - based on unsupervised, weakly supervised, and semisupervised algorithms - are used in order to maximize the sensitivity to unknown new physics signatures. These algorithms are applied to data corresponding to an integrated luminosity of 138more » fb^-1, recorded by the CMS experiment at the LHC, at a center-of-mass energy of 13 TeV. No significant excesses above background expectations are seen. Exclusion limits are derived on the production cross section of benchmark signal models varying in resonance mass, jet mass, and jet substructure. Many of these signatures have not been previously sought, making several of the limits reported on the corresponding benchmark models the first ever. When compared to benchmark inclusive and substructure-based search strategies, the anomaly detection methods are found to significantly enhance the sensitivity to a variety of models.« less

A measurement of the top quark pair ($$ \textrm{t}\overline{\textrm{t}} $$) production cross section in proton-proton collisions at a centre-of-mass energy of 5.02 TeV is presented. The data were collected at the LHC in autumn 2017, in dedicated runs with low-energy and low-intensity conditions with respect to the default configuration, and correspond to an integrated luminosity of 302 pb$$^{−1}$$. The measurement is performed using events with one electron or muon, and multiple jets, at least one of them being identified as originating from a b quark (b tagged). Events are classified based on the number of all reconstructed jets and ofmore » b-tagged jets. Multivariate analysis techniques are used to enhance the separation between the signal and backgrounds. The measured cross section is $$ 62.5\pm 1.6{\left(\textrm{stat}\right)}_{-2.5}^{+2.6}\left(\textrm{syst}\right)\pm 1.2\left(\textrm{lumi}\right) $$ pb. A combination with the result in the dilepton channel based on the same data set yields a value of 62.3 ± 1.5 (stat) ± 2.4 (syst) ± 1.2 (lumi) pb, to be compared with the standard model prediction of $$ {69.5}_{-3.7}^{+3.5} $$ pb at next-to-next-to-leading order in perturbative quantum chromodynamics.« less

A search is presented for rare decays of the Z and Higgs bosons to a photon and a J∕ψ or a ψ(2S) meson, with the charmonium state subsequentially decaying to a pair of muons. The data set corresponds to an integrated luminosity of 123 fb⁻¹ of proton-proton collisions at a center-of-mass energy of 13TeV collected with the CMS detector at the LHC. No evidence for branching fractions of these rare decay channels larger than predicted in the standard model is observed. Upper limits at 95% confidence level are set: $$\mathcal{B}$$(H → J∕ψγ ) < 2.6 × 10⁻⁴, $$\mathcal{B}$$(H → ψ(2S)γmore » ) < 9.9 × 10⁻⁴, $$\mathcal{B}$$(Z → J∕ψγ ) < 0.6 × 10⁻⁶, and $$\mathcal{B}$$(Z → ψ(2S)γ ) < 1.3 × 10⁻⁶. The ratio of the Higgs boson coupling modifiers 𝜅_c∕𝜅_γ is constrained to be in the interval (−157, +199) at 95% confidence level. Assuming 𝜅_γ = 1, this interval becomes (−166, +208).« less

Measurements are presented of inclusive and differential cross sections for Z boson associated production of top quark pairs ($$ \textrm{t}\overline{\textrm{t}}\textrm{Z} $$) and single top quarks (tZq or tWZ). The data were recorded in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$$^{−1}$$. Events with three or more leptons, electrons or muons, are selected and a multiclass deep neural network is used to separate three event categories, the $$ \textrm{t}\overline{\textrm{t}}\textrm{Z} $$ and tWZ processes, the tZq process, and the backgrounds. A profile likelihood approach is used to unfold the differential cross sections, tomore » account for systematic uncertainties, and to determine the correlations between the two signal categories in one global fit. The inclusive cross sections for a dilepton invariant mass between 70 and 110 GeV are measured to be 1.14 ± 0.07 pb for the sum of $$ \textrm{t}\overline{\textrm{t}}\textrm{Z} $$ and tWZ, and 0.81 ± 0.10 pb for tZq, in good agreement with theoretical predictions.[graphic not available: see fulltext]« less

A search is presented for a heavy resonance decaying into a Z boson and a Higgs (H) boson. The analysis is based on data from proton-proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 138 fb$$^{−1}$$, recorded with the CMS experiment in the years 2016–2018. Resonance masses between 1.4 and 5 TeV are considered, resulting in large transverse momenta of the Z and H bosons. Final states that result from Z boson decays to pairs of electrons, muons, or neutrinos are considered. The H boson is reconstructed as a single large-radius jet, recoiling againstmore » the Z boson. Machine-learning flavour-tagging techniques are employed to identify decays of a Lorentz-boosted H boson into pairs of charm or bottom quarks, or into four quarks via the intermediate H → WW$$^{*}$$ and ZZ$$^{*}$$ decays. The analysis targets H boson decays that were not generally included in previous searches using the H → $$ \textrm{b}\overline{\textrm{b}} $$ channel. Compared with previous analyses, the sensitivity for high resonance masses is improved significantly in the channel where at most one b quark is tagged.[graphic not available: see fulltext]« less

Three rare decay processes of the Higgs boson to a ρ(770)⁰, Φ(1020), or K^⁎(892)⁰ meson and a photon are searched for using $$\sqrt{s} = 13$$ TeV proton-proton collision data collected by the CMS experiment at the LHC. Events are selected assuming the mesons decay into a pair of charged pions, a pair of charged kaons, or a charged kaon and pion, respectively. Depending on the Higgs boson production mode, different triggering and reconstruction techniques are adopted. The analyzed data sets correspond to integrated luminosities up to 138 fb^-1, depending on the reconstructed final state. After combining various data sets andmore » categories, no significant excess above the background expectations is observed. Upper limits at 95% confidence level on the Higgs boson branching fractions into ρ(770)⁰$$γ$$, Φ(1020)$$γ$$, and K^⁎(892)⁰ are determined to be 3.7 x 10^-4, 3.0 x 10^-4, and 3.0 x 10^-4, respectively. In case of the ρ(770)⁰$$γ$$ and Φ(1020)$$γ$$ channels, these are the most stringent experimental limits to date.« less

A search is reported for charge-parity $CP$ violation in D$^0$$$$\to$$ K$$^0_\mathrm{S}$$K$$^0_\mathrm{S}$$ decays, using data collected in proton-proton collisions at $$\sqrt{s}$$ = 13 TeV recorded by the CMS experiment in 2018. The analysis uses a dedicated data set that corresponds to an integrated luminosity of 41.6 fb$$^{-1}$$, which consists of about 10 billion events containing a pair of b hadrons, nearly all of which decay to charm hadrons. The flavor of the neutral D meson is determined by the pion charge in the reconstructed decays D$$^{*+}$$$$\to$$ D$$^0\pi^+$$ and D$$^{*-}$$$$\to$$ D$$^0\pi^-$$. The $CP$ asymmetry in D$^0$$$$\to$$ K$$^0_\mathrm{S}$$K$$^0_\mathrm{S}$$ is measured to be $$A_{CP}$$(K$$^0_\mathrm{S}$$K$$^0_\mathrm{S}$$)more » = (6.2 $$\pm$$ 3.0 $$\pm$$ 0.2 $$\pm$$ 0.8)%, where the three uncertainties represent the statistical uncertainty, the systematic uncertainty, and the uncertainty in the measurement of the $CP$ asymmetry in the D$^0$ $$\to$$ K$$^0_\mathrm{S}\pi^+\pi^-$$ decay. This is the first $CP$ asymmetry measurement by CMS in the charm sector as well as the first to utilize a fully hadronic final state.« less