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A bstract A search for heavy neutral leptons (HNLs) of Majorana or Dirac type using proton-proton collision data at s = 13 TeV is presented. The data were collected by the CMS experiment at the CERN LHC and correspond to an integrated luminosity of 138 fb − 1 . Events with three charged leptons (electrons, muons, and hadronically decaying tau leptons) are selected, corresponding to HNL production in association with a charged lepton and decay of the HNL to two charged leptons and a standard model (SM) neutrino. The search is performed for HNL masses between 10 GeV and 1.5 TeV. No evidence for an HNL signal is observed in data. Upper limits at 95% confidence level are found for the squared coupling strength of the HNL to SM neutrinos, considering exclusive coupling of the HNL to a single SM neutrino generation, for both Majorana and Dirac HNLs. The limits exceed previously achieved experimental constraints for a wide range of HNL masses, and the limits on tau neutrino coupling scenarios with HNL masses above the W boson mass are presented for the first time.

A bstract A search for pairs of dijet resonances with the same mass is conducted in final states with at least four jets. Results are presented separately for the case where the four jet production proceeds via an intermediate resonant state and for nonresonant production. The search uses a data sample corresponding to an integrated luminosity of 138 fb − 1 collected by the CMS detector in proton-proton collisions at s = 13 TeV. Model-independent limits, at 95% confidence level, are reported on the production cross section of four-jet and dijet resonances. These first LHC limits on resonant pair production of dijet resonances via high mass intermediate states are applied to a signal model of diquarks that decay into pairs of vector-like quarks, excluding diquark masses below 7.6 TeV for a particular model scenario. There are two events in the tails of the distributions, each with a four-jet mass of 8 TeV and an average dijet mass of 2 TeV, resulting in local and global significances of 3.9 and 1.6 standard deviations, respectively, if interpreted as a signal. The nonresonant search excludes pair production of top squarks with masses between 0.50 TeV to 0.77 TeV, with the exception of a small interval between 0.52 and 0.58 TeV, for supersymmetric R -parity-violating decays to quark pairs, significantly extending previous limits. Here, the most significant excess above the predicted background occurs at an average dijet mass of 0.95 TeV, for which the local and global significances are 3.6 and 2.5 standard deviations, respectively.

A bstract A search for long-lived heavy neutrinos (N) in the decays of B mesons produced in proton-proton collisions at s = 13 TeV is presented. The data sample corresponds to an integrated luminosity of 41.6 fb − 1 collected in 2018 by the CMS experiment at the CERN LHC, using a dedicated data stream that enhances the number of recorded events containing B mesons. The search probes heavy neutrinos with masses in the range 1 < m N < 3 GeV and decay lengths in the range 10 − 2 < c τ N < 10 4 mm, where τ N is the N proper mean lifetime. Signal events are defined by the signature B → ℓ B NX; N → ℓ ± π ∓ , where the leptons ℓ B and ℓ can be either a muon or an electron, provided that at least one of them is a muon. The hadronic recoil system, X, is treated inclusively and is not reconstructed. No significant excess of events over the standard model background is observed in any of the ℓ ± π ∓ invariant mass distributions. Limits at 95% confidence level on the sum of the squares of the mixing amplitudes between heavy and light neutrinos, | V N | 2 , and on c τ N are obtained in different mixing scenarios for both Majorana and Dirac-like N particles. The most stringent upper limit |V N | 2 < 2.0 × 10 − 5 is obtained at m N = 1.95 GeV for the Majorana case where N mixes exclusively with muon neutrinos. The limits on |V N | 2 for masses 1 < m N < 1.7 GeV are the most stringent from a collider experiment to date.

A bstract A search for Higgs boson pair (HH) production in association with a vector boson V (W or Z boson) is presented. The search is based on proton-proton collision data at a center-of-mass energy of 13 TeV, collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb − 1 . Both hadronic and leptonic decays of V bosons are used. The leptons considered are electrons, muons, and neutrinos. The HH production is searched for in the b b ¯ b b ¯ decay channel. An observed (expected) upper limit at 95% confidence level of VHH production cross section is set at 294 (124) times the standard model prediction. Constraints are also set on the modifiers of the Higgs boson trilinear self-coupling, k λ , assuming k 2V = 1, and vice versa on the coupling of two Higgs bosons with two vector bosons, k 2V . The observed (expected) 95% confidence intervals of these coupling modifiers are − 37.7 < k λ < 37.2 ( − 30.1 < k λ < 28.9) and − 12.2 < k 2V < 13.5 ( − 7.2 < k 2V < 8.9), respectively.

A bstract A search is presented for the decay of the 125 GeV Higgs boson (H) to a pair of new light pseudoscalar bosons (a), followed by the prompt decay of each a boson to a bottom quark-antiquark pair, H → aa → b b ¯ b b ¯ . The analysis is performed using a data sample of proton-proton collisions collected with the CMS detector at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb − 1 . To reduce the background from standard model processes, the search requires the Higgs boson to be produced in association with a leptonically decaying W or Z boson. The analysis probes the production of new light bosons in a 15 < m a < 60 GeV mass range. Assuming the standard model predictions for the Higgs boson production cross sections for pp → WH and ZH, model independent upper limits at 95% confidence level are derived for the branching fraction B H → aa → b b ¯ b b ¯ . The combined WH and ZH observed upper limit on the branching fraction ranges from 1.10 for m a = 20 GeV to 0.36 for m a = 60 GeV, complementing other measurements in the μμττ , ττττ and bb ℓℓ ( ℓ = μ , τ ) channels.

A bstract A search for heavy, long-lived, charged particles with large ionization energy loss within the silicon tracker of the CMS experiment is presented. A data set of proton-proton collisions at a center of mass energy at s = 13 TeV, collected in 2017 and 2018 at the CERN LHC, corresponding to an integrated luminosity of 101 fb − 1 , is used in this analysis. Two different approaches for the search are taken. A new method exploits the independence of the silicon pixel and strips measurements, while the second method improves on previous techniques using ionization to determine a mass selection. No significant excess of events above the background expectation is observed. The results are interpreted in the context of the pair production of supersymmetric particles, namely gluinos, top squarks, and tau sleptons, and of the Drell-Yan pair production of fourth generation ( τ ′) leptons with an electric charge equal to or twice the absolute value of the electron charge ( e ). An interpretation of a Z’ boson decaying to two τ ′ leptons with an electric charge equal to 2 e is presented for the first time. The 95% confidence upper limits on the production cross section are extracted for each of these hypothetical particles.

A bstract Measurements of fiducial and total inclusive cross sections for W and Z boson production are presented in proton-proton collisions at s = 5.02 and 13 TeV. Electron and muon decay modes ( ℓ = e or μ ) are studied in the data collected with the CMS detector in 2017, in dedicated runs with reduced instantaneous luminosity. The data sets correspond to integrated luminosities of 298 ± 6 pb − 1 at 5.02 TeV and 206 ± 5 pb − 1 at 13 TeV. Measured values of the products of the total inclusive cross sections and the branching fractions at 5.02 TeV are σ (pp → W + X) B (W → ℓν ) = 7300 ± 10 (stat) ± 60 (syst) ± 140 (lumi) pb, and σ (pp → Z+X) B (Z → ℓ + ℓ − ) = 669 ± 2 (stat) ± 6 (syst) ± 13 (lumi) pb for the dilepton invariant mass in the range of 60–120 GeV. The corresponding results at 13 TeV are 20480 ± 10 (stat) ± 170 (syst) ± 470 (lumi) pb and 1952 ± 4 (stat) ± 18 (syst) ± 45 (lumi) pb. The measured values agree with cross section calculations at next-to-next-to-leading-order in perturbative quantum chromodynamics. Fiducial and total inclusive cross sections, ratios of cross sections of W + and W − production as well as inclusive W and Z boson production, and ratios of these measurements at 5.02 and 13 TeV are reported.

Despite the f 0 (980) hadron having been discovered half a century ago, the question about its quark content has not been settled: it might be an ordinary quark-antiquark ( q q ¯ ) meson, a tetraquark ( q q ¯ q q ¯ ) exotic state, a kaon-antikaon ( K K ¯ ) molecule, or a quark-antiquark-gluon ( q q ¯ g ) hybrid. This paper reports strong evidence that the f 0 (980) state is an ordinary q q ¯ meson, inferred from the scaling of elliptic anisotropies ( v 2 ) with the number of constituent quarks ( n q ), as empirically established using conventional hadrons in relativistic heavy ion collisions. The f 0 (980) state is reconstructed via its dominant decay channel f 0 (980) → π + π − , in proton-lead collisions recorded by the CMS experiment at the LHC, and its v 2 is measured as a function of transverse momentum ( p T ). It is found that the n q = 2 ( q q ¯ state) hypothesis is favored over n q = 4 ( q q ¯ q q ¯ or K K ¯ states) by 7.7, 6.3, or 3.1 standard deviations in the p T < 10, 8, or 6 GeV/ c ranges, respectively, and over n q = 3 ( q q ¯ g hybrid state) by 3.5 standard deviations in the p T < 8 GeV/ c range. This result represents the first determination of the quark content of the f 0 (980) state, made possible by using a novel approach, and paves the way for similar studies of other exotic hadron candidates. The quark structure of the f 0 (980) hadron is still unknown after 50 years of its discovery. Here, the CMS Collaboration reports a measurement of the elliptic flow of the f 0 (980) state in proton-lead collisions at a nucleon-nucleon centre-of-mass energy of 8.16 TeV, providing strong evidence that the state is an ordinary meson.

A bstract A standard model effective field theory (SMEFT) analysis with dimension-six operators probing nonresonant new physics effects is performed in the Higgs-strahlung process, where the Higgs boson is produced in association with a W or Z boson, in proton-proton collisions at a center-of-mass energy of 13 TeV. The final states in which the W or Z boson decays leptonically and the Higgs boson decays to a pair of bottom quarks are considered. The analyzed data were collected by the CMS experiment between 2016 and 2018 and correspond to an integrated luminosity of 138 fb − 1 . An approach designed to simultaneously optimize the sensitivity to Wilson coefficients of multiple SMEFT operators is employed. Likelihood scans as functions of the Wilson coefficients that carry SMEFT sensitivity in this final state are performed for different expansions in SMEFT. The results are consistent with the predictions of the standard model.

A bstract The results of a model-independent search for the pair production of new bosons within a mass range of 0 . 21 < m < 60 GeV, are presented. This study utilizes events with a four-muon final state. We use two data sets, comprising 41 . 5 fb − 1 and 59 . 7 fb − 1 of proton-proton collisions at s = 13 TeV, recorded in 2017 and 2018 by the CMS experiment at the CERN LHC. The study of the 2018 data set includes a search for displaced signatures of a new boson within the proper decay length range of 0 < cτ < 100 mm. Our results are combined with a previous CMS result, based on 35 . 9 fb − 1 of proton-proton collisions at s = 13 TeV collected in 2016. No significant deviation from the expected background is observed. Results are presented in terms of a model-independent upper limit on the product of cross section, branching fraction, and acceptance. The findings are interpreted across various benchmark models, such as an axion-like particle model, a vector portal model, the next-to-minimal supersymmetric standard model, and a dark supersymmetric scenario, including those predicting a non-negligible proper decay length of the new boson. In all considered scenarios, substantial portions of the parameter space are excluded, expanding upon prior results.