287 Search Results

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

A search is presented for a third-generation leptoquark (LQ) coupled exclusively to a τ lepton and a b quark. The search is based on proton-proton collision data at a center-of-mass energy of 13 TeV recorded with the CMS detector, corresponding to an integrated luminosity of 138 fb$$^{−1}$$. Events with τ leptons and a varying number of jets originating from b quarks are considered, targeting the single and pair production of LQs, as well as nonresonant t-channel LQ exchange. An excess is observed in the data with respect to the background expectation in the combined analysis of all search regions. Formore » a benchmark LQ mass of 2 TeV and an LQ-b-τ coupling strength of 2.5, the excess reaches a local significance of up to 2.8 standard deviations. Upper limits at the 95% confidence level are placed on the LQ production cross section in the LQ mass range 0.5–2.3 TeV, and up to 3 TeV for t-channel LQ exchange. Leptoquarks are excluded below masses of 1.22–1.88 TeV for different LQ models and varying coupling strengths up to 2.5. The study of nonresonant ττ production through t-channel LQ exchange allows lower limits on the LQ mass of up to 2.3 TeV to be obtained.[graphic not available: see fulltext]« 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 the lepton flavor violating $\mathrm{\tau }\to 3\mathrm{\mu }$ decay is performed using proton-proton collision events at a center-of-mass energy of 13 TeV collected by the CMS experiment at the LHC in 2017–2018, corresponding to an integrated luminosity of 97.7 ${\text{fb}}^{-1}$ . Tau leptons produced in both heavy-flavor hadron and W boson decays are exploited in the analysis. No evidence for the decay is observed. The results of this search are combined with an earlier null result based on data collected in 2016 to obtain a total integrated luminosity of 131more » ${\text{fb}}^{-1}$ . The observed (expected) upper limits on the branching fraction $\mathcal{B}(\mathrm{\tau }\to 3\mathrm{\mu })$ at confidence levels of 90 and 95% are $2.9\times {10}^{-8}$ ( $2.4\times {10}^{-8}$ ) and $3.6\times {10}^{-8}$ ( $3.0\times {10}^{-8}$ ), respectively.« less

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 $138{\mathrm{fb}}^{-1}$ . 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 anmore » up or charm quark. Events with an electron or a muon, 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: $\mathcal{B}(t\to u\gamma )<0.95\times {10}^{-5}$ ( $1.20\times {10}^{-5}$ ) and $\mathcal{B}(t\to c\gamma )<1.51\times {10}^{-5}$ ( $1.54\times {10}^{-5}$ ) at 95% confidence level, assuming a single nonzero coupling at a time. The obtained limit for $\mathcal{B}(t\to u\gamma )$ is similar to the current best limit, while the limit for $\mathcal{B}(t\to c\gamma )$ is significantly tighter than previous results.« 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