20 Search Results

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 for long-lived heavy neutrinos (N) in the decays of B mesons produced in proton-proton collisions at $$ \sqrt{s} $$ = 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$$^{−2}$$ < cτ$$_{N}$$ < 10$$^{4}$$ mm, where τ$$_{N}$$ is the N proper mean lifetime. Signalmore » 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 cτ$$_{N}$$ 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.[graphic not available: see fulltext]« less

A search for pair production of scalar and vector leptoquarks (LQs) each decaying to a muon and a bottom quark is performed using proton-proton collision data collected at $\sqrt{s}=13\mathrm{TeV}$ with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ . No excess above standard model expectation is observed. Scalar (vector) LQs with masses less than 1810 (2120) GeV are excluded at 95% confidence level, assuming a 100% branching fraction of the LQ decaying to a muon and a bottom quark. These limits represent the most stringent to date.

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

Measurements of the inclusive and differential fiducial cross sections for the Higgs boson production in the H → ZZ → 4ℓ (ℓ = e, μ) decay channel are presented. The results are obtained from the analysis of proton-proton collision data recorded by the CMS experiment at the CERN LHC at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$$^{−1}$$. The measured inclusive fiducial cross section is 2.73 ± 0.26 fb, in agreement with the standard model expectation of 2.86 ± 0.1 fb. Differential cross sections are measured as a function of several kinematic observables sensitivemore » to the Higgs boson production and decay to four leptons. A set of double-differential measurements is also performed, yielding a comprehensive characterization of the four leptons final state. Constraints on the Higgs boson trilinear coupling and on the bottom and charm quark coupling modifiers are derived from its transverse momentum distribution. All results are consistent with theoretical predictions from the standard model.« less

The production of a top quark-antiquark pair in association with a W boson ($$ \textrm{t}\overline{\textrm{t}}\textrm{W} $$) is measured in proton-proton collisions at a center-of-mass energy of 13 TeV. The analyzed data was recorded by the CMS experiment at the CERN LHC and corresponds to an integrated luminosity of 138 fb$$^{−1}$$. Events with two or three leptons (electrons and muons) and additional jets are selected. In events with two leptons, a multiclass neural network is used to distinguish between the signal and background processes. Events with three leptons are categorized based on the number of jets and of jets originating frommore » b quark hadronization, and the lepton charges. The inclusive $$ \textrm{t}\overline{\textrm{t}}\textrm{W} $$ production cross section in the full phase space is measured to be 868 ± 40(stat) ± 51(syst) fb. The $$ \textrm{t}\overline{\textrm{t}}\textrm{W} ^{+}$$ and $$ \textrm{t}\overline{\textrm{t}}\textrm{W} ^{−}$$ cross sections are also measured as 553 ± 30(stat) ± 30(syst) and 343 ± 26(stat) ± 25(syst) fb, respectively, and the corresponding ratio of the two cross sections is found to be $$ 1.61\pm 0.15{\left(\textrm{stat}\right)}_{-0.05}^{+0.07}\left(\textrm{syst}\right) $$. The measured cross sections are larger than but consistent with the standard model predictions within two standard deviations, and represent the most precise measurement of these cross sections to date.[graphic not available: see fulltext]« less

A search for nonresonant Higgs boson ($$H$$) pair production via gluon and vector boson ($$V$$) fusion is performed in the four-bottom-quark final state, using proton-proton collision data at 13 TeV corresponding to 138 fb$$^{−1}$$ collected by the CMS experiment at the LHC. The analysis targets Lorentz-boosted $$H$$ pairs identified using a graph neural network. It constrains the strengths relative to the standard model of the $$H$$ self-coupling and the quartic VVHH couplings, $$κ_{2V}$$, excluding $$κ_{2V} = 0$$ for the first time, with a significance of 6.3 standard deviations when other H couplings are fixed to their standard model values.

At the start of Run 2 in 2015, the LHC delivered proton-proton collisions at a center-of-mass energy of 13\TeV. During Run 2 (years 2015–2018) the LHC eventually reached a luminosity of 2.1× 1034 cm-2s-1, almost three times that reached during Run 1 (2009–2013) and a factor of two larger than the LHC design value, leading to events with up to a mean of about 50 simultaneous inelastic proton-proton collisions per bunch crossing (pileup). The CMS Level-1 trigger was upgraded prior to 2016 to improve the selection of physics events in the challenging conditions posed by the second run of the LHC.more » This paper describes the performance of the CMS Level-1 trigger upgrade during the data taking period of 2016–2018. The upgraded trigger implements pattern recognition and boosted decision tree regression techniques for muon reconstruction, includes pileup subtraction for jets and energy sums, and incorporates pileup-dependent isolation requirements for electrons and tau leptons. In addition, the new trigger calculates high-level quantities such as the invariant mass of pairs of reconstructed particles. The upgrade reduces the trigger rate from background processes and improves the trigger efficiency for a wide variety of physics signals.« less

The CMS muon detector system, muon reconstruction software, and high-level trigger underwent significant changes in 2013–2014 in preparation for running at higher LHC collision energy and instantaneous luminosity. The performance of the modified system is studied using proton-proton collision data at center-of-mass energy √s=13 TeV, collected at the LHC in 2015 and 2016. The measured performance parameters, including spatial resolution, efficiency, and timing, are found to meet all design specifications and are well reproduced by simulation. Despite the more challenging running conditions, the modified muon system is found to perform as well as, and in many aspects better than, previously.more » We dedicate this paper to the memory of Prof. Alberto Benvenuti, whose work was fundamental for the CMS muon detector.« less