114 Search Results

The first measurements of the Fourier coefficients ( $V_{n\mathrm{\Delta }}$ ) of the azimuthal distributions of charged hadrons emitted from photon-proton (γp) interactions are presented. The data are extracted from 68.8 nb⁻¹ of ultra-peripheral proton-lead (pPb) collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=8.16\text{TeV}$ using the CMS detector. The high energy lead ions produce a flux of photons that can interact with the oncoming proton. This γp system provides a set of uniquemore » initial conditions with multiplicity lower than in photon-lead collisions but comparable to recent electron-positron and electron-proton data. The $V_{n\mathrm{\Delta }}$ coefficients are presented in ranges of event multiplicity and transverse momentum ( $p_{\mathrm{T}}$ ) and are compared to corresponding hadronic minimum bias pPb results. For a given multiplicity range, the mean $p_{\mathrm{T}}$ of charged particles is smaller in γp than in pPb collisions. For both the γp and pPb samples, $V_{1\mathrm{\Delta }}$ is negative, $V_{2\mathrm{\Delta }}$ is positive, and $V_{3\mathrm{\Delta }}$ consistent with 0. For each multiplicity and $p_{\mathrm{T}}$ range, $V_{2\mathrm{\Delta }}$ is larger for γp events. The γp data are consistent with model predictions that have no collective effects.« less

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

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

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

Production cross sections of Image 1, Image 2, and Image 3 states decaying into Image 4 in proton-lead ( $\mathrm{p}\mathrm{Pb}$ ) collisions are reported using data collected by the CMS experiment at $\sqrt{s_{{}_{\mathrm{NN}}}}=5.02\text{TeV}$ . A comparison is made with corresponding cross sections obtained with $\mathrm{p}\mathrm{p}$ data measured at the same collision energy and scaled by the Pb nucleus mass number. The nuclear modification factor for Image 1 ismore » found to be Image 5. Similar results for the excited states indicate a sequential suppression pattern, such that Image 6. The suppression of all states is much less pronounced in $\mathrm{p}\mathrm{Pb}$ than in PbPb collisions, and independent of transverse momentum Image 7 and center-of-mass rapidity Image 8 of the individual Image 9 state in the studied range Image 10 and Image 11. Models that incorporate final-state effects of bottomonia in pPb collisions are in better agreement with the data than those which only assume initial-state modifications.« less

A search for physics beyond the standard model (SM) in final states with an electron or muon and missing transverse momentum is presented. The analysis uses data from proton-proton collisions at a centre-of-mass energy of 13 TeV, collected with the CMS detector at the LHC in 2016–2018 and corresponding to an integrated luminosity of 138 fb−1. No significant deviation from the SM prediction is observed. Model-independent limits are set on the production cross section of W’ bosons decaying into lepton-plus-neutrino final states. Within the framework of the sequential standard model, with the combined results from the electron and muon decaymore » channels a W’ boson with mass less than 5.7 TeV is excluded at 95% confidence level. Results on a SM precision test, the determination of the oblique electroweak W parameter, are presented using LHC data for the first time. These results together with those from the direct W’ resonance search are used to extend existing constraints on composite Higgs scenarios. This is the first experimental exclusion on compositeness parameters using results from LHC data other than Higgs boson measurements.« less

Results are presented from a search for physics beyond the standard model in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV in channels with two Higgs bosons, each decaying via the process H → b$$ \overline{\mathrm{b}} $$, and large missing transverse momentum. The search uses a data sample corresponding to an integrated luminosity of 137 fb$$^{−1}$$ collected by the CMS experiment at the CERN LHC. The search is motivated by models of supersymmetry that predict the production of neutralinos, the neutral partners of the electroweak gauge and Higgs bosons. The observed event yields in the signal regions are foundmore » to be consistent with the standard model background expectations. The results are interpreted using simplified models of supersymmetry. For the electroweak production of nearly mass-degenerate higgsinos, each of whose decay chains yields a neutralino $$ \left({\overset{\sim }{\upchi}}_1^0\right) $$ that in turn decays to a massless goldstino and a Higgs boson, $$ \left({\overset{\sim }{\upchi}}_1^0\right) $$ masses in the range 175 to 1025 GeV are excluded at 95% confidence level. For the strong production of gluino pairs decaying via a slightly lighter $$ \left({\overset{\sim }{\upchi}}_2^0\right) $$ to H and a light $$ \left({\overset{\sim }{\upchi}}_1^0\right) $$, gluino masses below 2330 GeV are excluded.[graphic not available: see fulltext]« less

Many measurements at the LHC require efficient identification of heavy-flavour jets, i.e. jets originating from bottom (b) or charm (c) quarks. An overview of the algorithms used to identify c jets is described and a novel method to calibrate them is presented. This new method adjusts the entire distributions of the outputs obtained when the algorithms are applied to jets of different flavours. It is based on an iterative approach exploiting three distinct control regions that are enriched with either b jets, c jets, or light-flavour and gluon jets. Results are presented in the form of correction factors evaluated usingmore » proton-proton collision data with an integrated luminosity of 41.5 fb$$^{-1}$$ at  √s = 13 TeV, collected by the CMS experiment in 2017. The closure of the method is tested by applying the measured correction factors on simulated data sets and checking the agreement between the adjusted simulation and collision data. Furthermore, a validation is performed by testing the method on pseudodata, which emulate various mismodelling conditions. The calibrated results enable the use of the full distributions of heavy-flavour identification algorithm outputs, e.g. as inputs to machine-learning models. Thus, they are expected to increase the sensitivity of future physics analyses.« less

A measurement of the cross section of the associated production of a single top quark and a W boson in final states with a muon or electron and jets in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV is presented. The data correspond to an integrated luminosity of 36 fb$$^{−1}$$ collected with the CMS detector at the CERN LHC in 2016. A boosted decision tree is used to separate the tW signal from the dominant t$$ \overline{\mathrm{t}} $$ background, whilst the subleading W+jets and multijet backgrounds are constrained using data-based estimates. This result is the first observation of themore » tW process in final states containing a muon or electron and jets, with a significance exceeding 5 standard deviations. The cross section is determined to be 89 ± 4 (stat) ± 12 (syst) pb, consistent with the standard model.[graphic not available: see fulltext]« less