75 Search Results

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 $$ \textrm{b}\overline{\textrm{b}}\textrm{b}\overline{\textrm{b}} $$ decay channel. An observed (expected) upper limit at 95% confidence level of VHH production cross section is set atmore » 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.[graphic not available: see fulltext]« less

The operation and performance of the Compact Muon Solenoid(CMS) electromagnetic calorimeter (ECAL) are presented, based ondata collected in pp collisions at√$$_{s}$$ =13 TeV at the CERN LHC, in the years from 2015 to 2018(LHC Run 2), corresponding to an integrated luminosity of151 fb$$^{-1}$$. The CMS ECAL is a scintillating lead-tungstatecrystal calorimeter, with a silicon strip preshower detector in theforward region that provides precise measurements of the energy andthe time-of-arrival of electrons and photons. The successfuloperation of the ECAL is crucial for a broad range of physics goals,ranging from observing the Higgs boson and measuring its properties,to other standard model measurements andmore » searches for newphenomena. Precise calibration, alignment, and monitoring of theECAL response are important ingredients to achieve these goals. Toface the challenges posed by the higher luminosity, whichcharacterized the operation of the LHC in Run 2, the proceduresestablished during the 2011–2012 run of the LHC have been revisitedand new methods have been developed for the energy measurement andfor the ECAL calibration. The energy resolution of the calorimeter,for electrons from Z boson decays reaching theECAL without significant loss of energy by bremsstrahlung, wasbetter than 1.8%, 3.0%, and 4.5% in the |η| intervals[0.0,0.8], [0.8,1.5], [1.5, 2.5], respectively. This resultingperformance is similar to that achieved during Run 1 in 2011–2012,in spite of the more severe running conditions.« less

A search for beyond the standard model spin-0 bosons, $\varphi$ , 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 $138{\mathrm{fb}}^{-1}more »$ . 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 $\varphi$ model, limits are set on the mixing angle of the Higgs boson with the $\varphi$ boson. For the associated production of a $\varphi$ 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.« less

The results of a search for stealth supersymmetry in final states with two photons and jets, targeting a phase space region with low missing transverse momentum ( $p_{\mathrm{T}}^{\mathrm{miss}}$ ), are reported. The study is based on a sample of proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$ collected by the CMS experiment, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . As LHC results continue to constrain the parameter spacemore » of the minimal supersymmetric standard model, the low $p_{\mathrm{T}}^{\mathrm{miss}}$ regime is increasingly valuable to explore. To estimate the backgrounds due to standard model processes in such events, we apply corrections derived from simulation to an estimate based on a control selection in data. The results are interpreted in the context of simplified stealth supersymmetry models with gluino and squark pair production. The observed data are consistent with the standard model predictions, and gluino (squark) masses of up to 2150 (1850) GeV are excluded at the 95% confidence level.« less

Since the initial data taking of the CERN LHC, the CMSexperiment has undergone substantial upgrades and improvements. Thispaper discusses the CMS detector as it is configured for the thirddata-taking period of the CERN LHC, Run 3, which started in2022. The entire silicon pixel tracking detector was replaced. A newpowering system for the superconducting solenoid was installed. Theelectronics of the hadron calorimeter was upgraded. All the muonelectronic systems were upgraded, and new muon detector stationswere added, including a gas electron multiplier detector. Theprecision proton spectrometer was upgraded. The dedicated luminositydetectors and the beam loss monitor were refurbished. Substantialimprovements to the trigger, datamore » acquisition, software, andcomputing systems were also implemented, including a new hybridCPU/GPU farm for the high-level trigger.« less

A search for exotic decays of the Higgs boson ($$\text {H}$$) with a mass of 125$$\,\text {Ge}\hspace{-.08em}\text {V}$$ to a pair of light pseudoscalars $$\text {a}_{1} $$ is performed in final states where one pseudoscalar decays to two $${\textrm{b}}$$ quarks and the other to a pair of muons or $$\tau $$ leptons. A data sample of proton–proton collisions at $$\sqrt{s}=13\,\text {Te}\hspace{-.08em}\text {V} $$ corresponding to an integrated luminosity of 138$$\,\text {fb}^{-1}$$ recorded with the CMS detector is analyzed. No statistically significant excess is observed over the standard model backgrounds. Upper limits are set at 95% confidence level ($$\text {CL}$$) onmore » the Higgs boson branching fraction to $$\upmu \upmu \text{ b } \text{ b } $$ and to $$\uptau \uptau \text{ b } \text{ b },$$ via a pair of $$\text {a}_{1} $$s. The limits depend on the pseudoscalar mass $$m_{\text {a}_{1}}$$ and are observed to be in the range (0.17–3.3) $$\times 10^{-4}$$ and (1.7–7.7) $$\times 10^{-2}$$ in the $$\upmu \upmu \text{ b } \text{ b } $$ and $$\uptau \uptau \text{ b } \text{ b } $$ final states, respectively. In the framework of models with two Higgs doublets and a complex scalar singlet (2HDM+S), the results of the two final states are combined to determine upper limits on the branching fraction $${\mathcal {B}}(\text {H} \rightarrow \text {a}_{1} \text {a}_{1} \rightarrow \ell \ell \text{ b } \text{ b})$$ at 95% $$\text {CL}$$, with $$\ell $$ being a muon or a $$\uptau $$ lepton. For different types of 2HDM+S, upper bounds on the branching fraction $${\mathcal {B}}(\text {H} \rightarrow \text {a}_{1} \text {a}_{1} )$$ are extracted from the combination of the two channels. In most of the Type II 2HDM+S parameter space, $${\mathcal {B}}(\text {H} \rightarrow \text {a}_{1} \text {a}_{1} )$$ values above 0.23 are excluded at 95% $$\text {CL}$$ for $$m_{\text {a}_{1}}$$ values between 15 and 60$$\,\text {Ge}\hspace{-.08em}\text {V}$$.« less

A measurement is presented of the primary Lund jet plane (LJP) density in inclusive jet production in proton-proton collisions. The analysis uses 138 fb$$^{−1}$$ of data collected by the CMS experiment at $$ \sqrt{s} $$ = 13 TeV. The LJP, a representation of the phase space of emissions inside jets, is constructed using iterative jet declustering. The transverse momentum k$$_{T}$$ and the splitting angle ∆R of an emission relative to its emitter are measured at each step of the jet declustering process. The average density of emissions as function of ln(k$$_{T}$$/GeV) and ln(R/∆R) is measured for jets with distance parametersmore » R = 0.4 or 0.8, transverse momentum p$$_{T}$$> 700 GeV, and rapidity |y| < 1.7. The jet substructure is measured using the charged-particle tracks of the jet. The measured distributions, unfolded to the level of stable charged particles, are compared with theoretical predictions from simulations and with perturbative quantum chromodynamics calculations. Due to the ability of the LJP to factorize physical effects, these measurements can be used to improve different aspects of the physics modeling in event generators.[graphic not available: see fulltext]« less

Measurements of inclusive and normalized differential cross sections of the associated production of top quark-antiquark and bottom quark-antiquark pairs, $$ \textrm{t}\overline{\textrm{t}}\textrm{b}\overline{\textrm{b}} $$, are presented. The results are based on data from proton-proton collisions collected by the CMS detector at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$$^{−1}$$. The cross sections are measured in the lepton+jets decay channel of the top quark pair, using events containing exactly one isolated electron or muon and at least five jets. Measurements are made in four fiducial phase space regions, targeting different aspects of the $$ \textrm{t}\overline{\textrm{t}}\textrm{b}\overline{\textrm{b}} $$ process.more » Distributions are unfolded to the particle level through maximum likelihood fits, and compared with predictions from several event generators. The inclusive cross section measurements of this process in the fiducial phase space regions are the most precise to date. In most cases, the measured inclusive cross sections exceed the predictions with the chosen generator settings. The only exception is when using a particular choice of dynamic renormalization scale, $$ {\mu}_{\textrm{R}}=\frac{1}{2}{\prod}_{i=\textrm{t},\overline{\textrm{t}},\textrm{b},\overline{\textrm{b}}}{m}_{\textrm{T},i}^{1/4} $$, where $$ {m}_{\textrm{T},i}^2={m}_i^2+{p}_{\textrm{T},i}^2 $$ are the transverse masses of top and bottom quarks. The differential cross sections show varying degrees of compatibility with the theoretical predictions, and none of the tested generators with the chosen settings simultaneously describe all the measured distributions.[graphic not available: see fulltext]« less

A search for W′ bosons decaying to a top and a bottom quark in final states including an electron or a muon is performed with the CMS detector at the LHC. The analyzed data correspond to an integrated luminosity of 138 fb$$^{−1}$$ of proton-proton collisions at a center-of-mass energy of 13 TeV. Good agreement with the standard model expectation is observed and no evidence for the existence of the W′ boson is found over the mass range examined. The largest observed deviation from the standard model expectation is found for a W′ boson mass ($$ {m}_{{\textrm{W}}^{\prime }} $$) hypothesis ofmore » 3.8 TeV with a relative decay width of 1%, with a local (global) significance of 2.6 (2.0) standard deviations. Upper limits on the production cross sections of W′ bosons decaying to a top and a bottom quark are set. Left- and right-handed W′ bosons with $$ {m}_{{\textrm{W}}^{\prime }} $$ below 3.9 and 4.3 TeV, respectively, are excluded at the 95% confidence level, under the assumption that the new particle has a narrow decay width. Limits are also set for relative decay widths up to 30%.[graphic not available: see fulltext]« less

A search for dark matter particles is performed using events with a pair of W bosons and large missing transverse momentum. Candidate events are selected by requiring one or two leptons (ℓ = electrons or muons). The analysis is based on proton-proton collision data collected at a center-of-mass energy of 13 TeV by the CMS experiment at the LHC and corresponding to an integrated luminosity of 138 fb$$^{−1}$$. No significant excess over the expected standard model background is observed in the ℓνqq and 2ℓ2ν final states of the W$$^{+}$$W$$^{−}$$ boson pair. Limits are set on dark matter production in themore » context of a simplified dark Higgs model, with a dark Higgs boson mass above the W$$^{+}$$W$$^{−}$$ mass threshold. The dark matter phase space is probed in the mass range 100–300 GeV, extending the scope of previous searches. Current exclusion limits are improved in the range of dark Higgs masses from 160 to 250 GeV, for a dark matter mass of 200 GeV.[graphic not available: see fulltext]« less