272 Search Results

A search for the exotic decay of the Higgs boson to a pair of light pseudoscalars, each of which subsequently decays into a pair of photons, is presented. The search uses data from proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV recorded with the CMS detector at the LHC that corresponds to an integrated luminosity of 132 fb$$^{−1}$$. The analysis probes pseudoscalar bosons with masses in the range 15–62 GeV, coming from the Higgs boson decay, which leads to four well-isolated photons in the final state. No significant deviation from the background-only hypothesis is observed. Upper limits are setmore » on the product of the Higgs boson production cross section and branching fraction into four photons. The observed (expected) limits range from 0.80 (1.00) fb for a pseudoscalar boson mass of 15 GeV to 0.26 (0.24) fb for a mass of 62 GeV at 95% confidence level.[graphic not available: see fulltext]« less

A search for the direct production of a pair of $$τ$$ sleptons, the supersymmetric partners of $$τ$$ leptons, is presented. Each $$τ$$ slepton is assumed to decay to a $$τ$$ lepton and the lightest supersymmetric particle (LSP), which is assumed to be stable and to not interact in the detector, leading to an imbalance in the total reconstructed transverse momentum. The search is carried out in events identified as containing two $$τ$$ leptons, each decaying to one or more hadrons and a neutrino, and significant transverse momentum imbalance. In addition to scenarios in which the $$τ$$ sleptons decay promptly, themore » search also addresses scenarios in which the $$τ$$ sleptons have sufficiently long lifetimes to give rise to nonprompt $$τ$$ leptons. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC with the CMS detector in 2016–2018, and correspond to an integrated luminosity of 138 fb^-1. No significant excess is seen with respect to standard model expectations. Upper limits on cross sections for the pair production of $$τ$$ sleptons are obtained in the framework of simplified models. In a scenario in which the $$τ$$ sleptons are superpartners of left-handed $$τ$$ leptons, and each undergoes a prompt decay to a $$τ$$ lepton and a nearly massless LSP, $$τ$$ slepton masses between 115 and 340 GeV are excluded. In a scenario in which the lifetime of the $$τ$$ sleptons corresponds to c$$τ$$₀ = 0.1 mm, where $$τ_{0}$$ represents the mean proper lifetime of the $$τ$$ slepton, masses between 150 and 220 GeV are excluded.« less

The double differential cross sections of the Drell–Yan lepton pair ($$\ell^+\ell^-$$, dielectron or dimuon) production are measured as functions of the invariant mass m$$_{\ell\ell}$$, transverse momentum p_T($$\ell\ell$$), and $$\varphi^{*}_{\eta}$$. The observable, derived from angular measurements of the leptons and highly correlated with p_T($$\ell\ell$$), is used to probe the low-p_T region in a complementary way. Dilepton masses up to 1 TeV are investigated. Additionally, a measurement is performed requiring at least one jet in the final state. To benefit from partial cancellation of the systematic uncertainty, the ratios of the differential cross sections for various m$$_{\ell\ell}$$ ranges to those in themore » Z mass peak interval are presented. The collected data correspond to an integrated luminosity of 36.3 fb^-1 of proton–proton collisions recorded with the CMS detector at the LHC at a centre-of-mass energy of 13 TeV. Measurements are compared with predictions based on perturbative quantum chromodynamics, including soft-gluon resummation.« less

A search is performed for narrow resonances decaying to final states of two jets, with at least one jet originating from a $b$ quark, in proton-proton collisions at $\sqrt{s}=13\mathrm{TeV}$. The data set corresponds to an integrated luminosity of $138{\mathrm{fb}}^{-1}$ collected with the CMS detector at the LHC. Jets originating from energetic $b$ hadrons are identified through a $b$-tagging algorithm that utilizes a deep neural network or the presence of a muon inside a jet. The invariant mass spectrum of jet pairsmore » is well described by a smooth parametrization and no evidence for the production of new particles is observed. Upper limits on the production cross section are set for excited $b$ quarks and other resonances decaying to dijet final states containing $b$ quarks. These limits exclude at 95% confidence level models of $Z^{\text{'}}$ bosons with masses from 1.8 TeV to 2.4 TeV and of excited $b$ quarks with masses from 1.8 TeV to 4.0 TeV. This is the most stringent exclusion of excited $b$ quarks to date.« less

New sets of parameter tunes for two of the colour reconnection models, quantum chromodynamics-inspired and gluon-move, implemented in the PYTHIA 8 event generator, are obtained based on the default CMS PYTHIA 8 underlying-event tune, CP5. Measurements sensitive to the underlying event performed by the CMS experiment at centre-of-mass energies $$\sqrt{s}=$$7 and 13 TeV, and by the CDF experiment at 1.96 TeV are used to constrain the parameters of colour reconnection models and multiple-parton interactions simultaneously. The new colour reconnection tunes are compared with various measurements at 1.96, 7, 8, and 13 TeV including measurements of the underlying-event, strange-particle multiplicities, jetmore » substructure observables, jet shapes, and colour flow in top quark pair ($$t\bar{t}$$) events. The new tunes are also used to estimate the uncertainty related to colour reconnection modelling in the top quark mass measurement using the decay products of $$t\bar{t}$$ events in the semileptonic channel at 13 TeV .« less

A search is reported for pairs of light Higgs bosons (H₁) produced in supersymmetric cascade decays in final states with small missing transverse momentum. A data set of LHC pp collisions collected with the CMS detector at $$\sqrt{s}$$ = 13 TeV and corresponding to an integrated luminosity of 138 fb^-1 is used. The search targets events where both H₁ bosons decay into $$\text{b}\bar{\text{b}}$$ pairs that are reconstructed as large-radius jets using substructure techniques. No evidence is found for an excess of events beyond the background expectations of the standard model (SM). Results from the search are interpreted in the next-to-minimalmore » supersymmetric extension of the SM, where a “singlino” of small mass leads to squark and gluino cascade decays that can predominantly end in a highly Lorentz-boosted singlet-like H₁ and a singlino-like neutralino of small transverse momentum. Upper limits are set on the product of the squark or gluino pair production cross section and the square of the branching fraction of the $$\text{b}\bar{\text{b}}$$ in a benchmark model containing almost mass-degenerate gluinos and light-flavour squarks. Under the assumption of an SM-like H₁ → $$\text{b}\bar{\text{b}}$$ branching fraction, H₁ bosons with masses in the range 40–120 GeV arising from the decays of squarks or gluinos with a mass of 1200–2500 GeV are excluded at 95% confidence level.« less

Results are presented from a search for CP violation in top quark pair production, using proton-proton collisions at a center-of-mass energy of 13 TeV. The data used for this analysis consist of final states with two charged leptons collected by the CMS experiment, and correspond to an integrated luminosity of 35.9 fb$$^{−1}$$. The search uses two observables, $$ \mathcal{O} _{1}$$ and $$ \mathcal{O} _{3}$$, which are Lorentz scalars. The observable $$ \mathcal{O} _{1}$$ is constructed from the four-momenta of the charged leptons and the reconstructed top quarks, while $$ \mathcal{O} _{3}$$ consists of the four-momenta of the charged leptons andmore » the b quarks originating from the top quarks. Asymmetries in these observables are sensitive to CP violation, and their measurement is used to determine the chromoelectric dipole moment of the top quark. The results are consistent with the expectation from the standard model.[graphic not available: see fulltext]« less

Measurements of Higgs boson production, where the Higgs boson decays into a pair of τ leptons, are presented, using a sample of proton-proton collisions collected with the CMS experiment at a center-of-mass energy of , corresponding to an integrated luminosity of 138 fb^–1. Three analyses are presented. Two are targeting Higgs boson production via gluon fusion and vector boson fusion: a neural network based analysis and an analysis based on an event categorization optimized on the ratio of signal over background events. These are complemented by an analysis targeting vector boson associated Higgs boson production. Results are presented in themore » form of signal strengths relative to the standard model predictions and products of cross sections and branching fraction to τ leptons, in up to 16 different kinematic regions. For the simultaneous measurements of the neural network based analysis and the analysis targeting vector boson associated Higgs boson production signal strengths are found to be 0.82 ± 0.11 for inclusive Higgs boson production, 0.67 ± 0.19 (0.81 ± 0.17) for the production mainly via gluon fusion (vector boson fusion), and 1.79 ± 0.45 for vector boson associated Higgs boson production.« less

Results are presented from a search for the Higgs boson decay H → Zγ, where Z → ℓ$$^{+}$$ℓ$$^{−}$$ with ℓ = e or μ. The search is performed using a sample of proton-proton (pp) collision data at a center-of-mass energy of 13 TeV, recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 138 fb$$^{−1}$$. Events are assigned to mutually exclusive categories, which exploit differences in both event topology and kinematics of distinct Higgs production mechanisms to enhance signal sensitivity. The signal strength μ, defined as the product of the cross section and the branching fractionmore » $$ \left[\sigma \left(\textrm{pp}\to \textrm{H}\right)\mathcal{B}\left(\textrm{H}\to \textrm{Z}\upgamma \right)\right] $$ relative to the standard model prediction, is extracted from a simultaneous fit to the ℓ$$^{+}$$ℓ$$^{−}$$γ invariant mass distributions in all categories and is measured to be μ = 2.4 ± 0.9 for a Higgs boson mass of 125.38 GeV. The statistical significance of the observed excess of events is 2.7 standard deviations. This measurement corresponds to $$ \left[\sigma \left(\textrm{pp}\to \textrm{H}\right)\mathcal{B}\left(\textrm{H}\to \textrm{Z}\upgamma \right)\right]=0.21\pm 0.08 $$ pb. The observed (expected) upper limit at 95% confidence level on μ is 4.1 (1.8), where the expected limit is calculated under the background-only hypothesis. The ratio of branching fractions $$ \mathcal{B}\left(\textrm{H}\to \textrm{Z}\upgamma \right)/\mathcal{B}\left(\textrm{H}\to \upgamma \upgamma \right) $$ is measured to be $$ {1.5}_{-0.6}^{+0.7} $$, which agrees with the standard model prediction of 0.69 ± 0.04 at the 1.5 standard deviation level.[graphic not available: see fulltext]« less

A precise measurement of the invisible width of the Z boson produced in proton-proton collisions at a center-of-mass energy of 13 TeV is presented using data recorded by the CMS experiment at the LHC, corresponding to an integrated luminosity of 36.3 ${\text{fb}}^{-1}$ . The result is obtained from a simultaneous fit to kinematic distributions for two data samples of Z boson plus jets: one dominated by Z boson decays to invisible particles and the other by Z boson decays to muon and electron pairs. The invisible width is measured to be $more »$ 523±3(stat)±16(syst)MeV . This result is the first precise measurement of the invisible width of the Z boson at a hadron collider, and is the single most precise direct measurement to date, competitive with the combined result of the direct measurements from the LEP experiments.« less