127 Search Results

A direct search for electroweak production of charginos and neutralinos is presented. Events with three or four leptons, with up to two hadronically decaying $$\tau$$ leptons, or two same-sign light leptons are analyzed. The data sample consists of 137 fb$$^{-1}$$ of proton-proton collisions with a center of mass energy of 13 TeV, recorded with the CMS detector at the LHC. The results are interpreted in terms of several simplified models. These represent a broad range of production and decay scenarios for charginos and neutralinos. A parametric neural network is used to target several of the models with large backgrounds. Inmore » addition, results using orthogonal search regions are provided for all the models, simplifying alternative theoretical interpretations of the results. Depending on the model hypotheses, charginos and neutralinos with masses up to values between 300 and 1450 GeV are excluded at 95% confidence level.« less

A search for low-mass dilepton resonances in Higgs boson decays is conducted in the four-lepton final state. The decay is assumed to proceed via a pair of beyond the standard model particles, or one such particle and a $${\mathrm{Z}}$$ boson. The search uses proton–proton collision data collected with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 137$$\,\text {fb}^{-1}$$, at a center-of-mass energy $$\sqrt{s} = 13\,\text {TeV} $$. No significant deviation from the standard model expectation is observed. Upper limits at 95% confidence level are set on model-independent Higgs boson decay branching fractions. Additionally, limits onmore » dark photon and axion-like particle production, based on two specific models, are reported.« less

The cross sections for inclusive and Mueller-Navelet dijet production are measured as a function of the rapidity separation between the jets in proton-proton collisions at $$\sqrt{s}$$ = 2.76 TeV for jets with transverse momentum p_T > 35 GeV and rapidity |y| < 4.7. Various dijet production cross section ratios are also measured. A veto on additional jets with p_T > 20 GeV is introduced to improve the sensitivity to the effects of the Balitsky-Fadin-Kuraev-Lipatov (BFKL) evolution. The measurement is compared with the predictions of various Monte Carlo models based on leading-order and next-to-leading-order calculations including the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi leading-logarithm (LL) partonmore » shower as well as the LL BFKL resummation.« less

A search for dark matter in the form of strongly interacting massive particles (SIMPs) using the CMS detector at the LHC is presented. The SIMPs would be produced in pairs that manifest themselves as pairs of jets without tracks. The energy fraction of jets carried by charged particles is used as a key discriminator to suppress efficiently the large multijet background, and the remaining background is estimated directly from data. The search is performed using proton–proton collision data corresponding to an integrated luminosity of 16.1 fb^-1, collected with the CMS detector in 2016. No significant excess of events is observedmore » above the expected background. For the simplified dark matter model under consideration, SIMPs with masses up to 100 GeV are excluded and further sensitivity is explored towards higher masses.« less

A search for W$$\gamma$$ resonances in the mass range between 0.7 and 6.0 TeV is presented. The W boson is reconstructed via its hadronic decays, with the final-state products forming a single large-radius jet, owing to a high Lorentz boost of the W boson. The search is based on proton-proton collision data at $$\sqrt{s} = $$ 13 TeV, corresponding to an integrated luminosity of 137 fb$$^{-1}$$, collected with the CMS detector at the LHC in 2016-2018. The W$$\gamma$$ mass spectrum is parameterized with a smoothly falling background function and examined for the presence of resonance-like signals. No significant excess abovemore » the predicted background is observed. Model-specific upper limits at 95% confidence level on the product of the cross section and branching fraction to the W$$\gamma$$ channel are set. Limits for narrow resonances and for resonances with an intrinsic width equal to 5% of their mass, for spin-0 and spin-1 hypotheses, range between 0.17 fb at 6.0 TeV and 55 fb at 0.7 TeV. These are the most restrictive limits to date on the existence of such resonances. In specific narrow-resonance benchmark models, heavy scalar (vector) triplet resonances with masses between 0.75 (1.15) and 1.40 (1.36) TeV are excluded for a range of model parameters. Model-independent limits on the product of the cross section, signal acceptance, and branching fraction to the W$$\gamma$$ channel are set for minimum W$$\gamma$$ mass thresholds between 1.5 and 8.0 TeV.« less

Collinear (small-angle) and large-angle, as well as soft and hard radiations are investigated in three-jet and Z + two-jet events collected in proton-proton collisions at the LHC. The normalized production cross sections are measured as a function of the ratio of transverse momenta of two jets and their angular separation. The measurements in the three-jet and Z + two-jet events are based on data collected at a center-of-mass energy of 8TeV, corresponding to an integrated luminosity of 19.8fb^-1. The Z + two-jet events are reconstructed in the dimuon decay channel of the Z boson. The three-jet measurement is extended tomore » include $$\sqrt {s}$$=13TeV data corresponding to an integrated luminosity of 2.3fb^-1. The results are compared to predictions from event generators that include parton showers, multiple parton interactions, and hadronization. The collinear and soft regions are in general well described by parton showers, whereas the regions of large angular separation are often best described by calculations using higher-order matrix elements.« less

A search is performed for W' bosons decaying to a top and a bottom quark in the all-hadronic final state, in proton-proton collisions at a center-of-mass energy of 13 TeV. The analyzed data were collected by the CMS experiment between 2016 and 2018 and correspond to an integrated luminosity of 137 fb^-1. Deep neural network algorithms are used to identify the jet initiated by the bottom quark and the jet containing the decay products of the top quark when the W' boson from the top quark decays hadronically. No excess above the estimated standard model background is observed. Upper limitsmore » on the production cross sections of W' bosons decaying to a top and a bottom quark are set. Both left- and right-handed W' bosons with masses below 3.4 TeV are excluded at 95% confidence level, and the most stringent limits to date on W bosons decaying to a top and a bottom quark in the all-hadronic final state are obtained.« less

The measurement of the luminosity recorded by the CMS detector installed at LHC interaction point 5, using proton–proton collisions at √s = 13 TeV in 2015 and 2016, is reported. The absolute luminosity scale is measured for individual bunch crossings using beam-separation scans (the van der Meer method), with a relative precision of 1.3 and 1.0% in 2015 and 2016, respectively. The dominant sources of uncertainty are related to residual differences between the measured beam positions and the ones provided by the operational settings of the LHC magnets, the factorizability of the proton bunch spatial density functions in the coordinatesmore » transverse to the beam direction, and the modeling of the effect of electromagnetic interactions among protons in the colliding bunches. When applying the van der Meer calibration to the entire run periods, the integrated luminosities when CMS was fully operational are 2.27 and 36.3 fb^-1 in 2015 and 2016, with a relative precision of 1.6 and 1.2%, respectively. These are among the most precise luminosity measurements at bunched-beam hadron colliders.« less

A search for charged Higgs bosons produced in vector boson fusion processes and decaying into vector bosons, using proton–proton collisions at √s = 13 TeV at the LHC, is reported. The data sample corresponds to an integrated luminosity of 137 fb^-1 collected with the CMS detector. Events are selected by requiring two or three electrons or muons, moderate missing transverse momentum, and two jets with a large rapidity separation and a large dijet mass. No excess of events with respect to the standard model background predictions is observed. Model independent upper limits at 95% confidence level are reported on themore » product of the cross section and branching fraction for vector boson fusion production of charged Higgs bosons as a function of mass, from 200 to 3000GeV. The results are interpreted in the context of the Georgi–Machacek model.« less

The first measurement of the inclusive cross section for top quark pairs ($$t\bar{t}$$) produced in association with two additional charm jets is presented. The analysis uses the dileptonic final states of $$t\bar{t}$$ events produced in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data correspond to an integrated luminosity of 41.5 fb^-1 recorded by the CMS experiment at the LHC. A new charm jet identification algorithm provides input to a neural network that is trained to distinguish among $$t\bar{t}$$ events with two additional charm ($$t\bar{t}c\bar{c}$$), bottom ($$t\bar{t}b\bar{b}$$), and light-flavour or gluon ($$t\bar{t}LL$$) jets. By means of a templatemore » fitting procedure, the inclusive $$t\bar{t}c\bar{c}$$, $$t\bar{t}b\bar{b}$$, and $$t\bar{t}LL$$ cross sections are simultaneously measured, together with their ratios to the inclusive $$t\bar{t}$$ + two jets cross section. This provides measurements of the $$t\bar{t}c\bar{c}$$ and $$t\bar{t}b\bar{b}$$ cross sections of 10.1 ± 1.2 (stat) ± 1.4 (syst) pb and 4.54 ± 0.35 (stat) ± 0.56 (syst) pb, respectively, in the full phase space. The results are compared and found to be consistent with predictions from two different matrix element generators with next-to-leading order accuracy in quantum chromodynamics, interfaced with a parton shower simulation.« less