413 Search Results

Abstract A search for heavy, long-lived, charged particles with large ionization energy loss within the silicon tracker of the CMS experiment is presented. A data set of proton-proton collisions at a center of mass energy at $$$$ \sqrt{s} $$$$ s = 13 TeV, collected in 2017 and 2018 at the CERN LHC, corresponding to an integrated luminosity of 101 fb −1, is used in this analysis. Two different approaches for the search are taken. A new method exploits the independence of the silicon pixel and strips measurements, while the second method improves on previousmore » techniques using ionization to determine a mass selection. No significant excess of events above the background expectation is observed. The results are interpreted in the context of the pair production of supersymmetric particles, namely gluinos, top squarks, and tau sleptons, and of the Drell-Yan pair production of fourth generation (τ′) leptons with an electric charge equal to or twice the absolute value of the electron charge (e). An interpretation of a Z’ boson decaying to two τ′ leptons with an electric charge equal to 2e is presented for the first time. The 95% confidence upper limits on the production cross section are extracted for each of these hypothetical particles.« less

A search is presented for rare decays of the Z and Higgs bosons to a photon and a J∕ψ or a ψ(2S) meson, with the charmonium state subsequentially decaying to a pair of muons. The data set corresponds to an integrated luminosity of 123 fb⁻¹ of proton-proton collisions at a center-of-mass energy of 13TeV collected with the CMS detector at the LHC. No evidence for branching fractions of these rare decay channels larger than predicted in the standard model is observed. Upper limits at 95% confidence level are set: $$\mathcal{B}$$(H → J∕ψγ ) < 2.6 × 10⁻⁴, $$\mathcal{B}$$(H → ψ(2S)γmore » ) < 9.9 × 10⁻⁴, $$\mathcal{B}$$(Z → J∕ψγ ) < 0.6 × 10⁻⁶, and $$\mathcal{B}$$(Z → ψ(2S)γ ) < 1.3 × 10⁻⁶. The ratio of the Higgs boson coupling modifiers 𝜅_c∕𝜅_γ is constrained to be in the interval (−157, +199) at 95% confidence level. Assuming 𝜅_γ = 1, this interval becomes (−166, +208).« less

The TOTEM Roman pot detectors are used to reconstruct the transverse momentum of scattered protons and to estimate the transverse location of the primary interaction. This paper presents new methods of track reconstruction, measurements of strip-level detection efficiencies, cross-checks of the LHC beam optics, and detector alignment techniques, along with their application in the selection of signal collision events. The track reconstruction is performed by exploiting hit cluster information through a novel method using a common polygonal area in the intercept-slope plane. The technique is applied in the relative alignment of detector layers with μm precision. A tag-and-probe method ismore » used to extract strip-level detection efficiencies. The alignment of the Roman pot system is performed through time-dependent adjustments, resulting in a position accuracy of 3 μm in the horizontal and 60 μm in the vertical directions. The goal is to provide an optimal reconstruction tool for central exclusive physics analyses based on the high-β* data-taking period at $$\sqrt({s})$$ = 13 TeV in 2018.« less

An analysis is presented based on models of the intrinsic transverse momentum (intrinsic 𝑘_T) of partons in nucleons by studying the dilepton transverse momentum in Drell-Yan events. Using parameter tuning in event generators and existing data from fixed-target experiments and from hadron colliders, our investigation spans 3 orders of magnitude in center-of-mass energy and 2 orders of magnitude in dilepton invariant mass. The results show an energy-scaling behavior of the intrinsic 𝑘_T parameters, independent of the dilepton invariant mass at a given center-of-mass energy.

A search is presented for fractionally charged particles with charges below 1⁢𝑒, using their small energy loss in the tracking detector as a key variable to observe a signal. The analyzed dataset corresponds to an integrated luminosity of 138 fb⁻¹ of proton-proton collisions collected at $$\sqrt{𝑠}$$ = 13 TeV in 2016–2018 at the CERN LHC. This is the first search at the LHC for new particles with a charge between 𝑒/3 and 0.9⁢𝑒, including an extension of previous results at a charge of 2⁢𝑒/3. Masses up to 640 GeV and charges as low as 𝑒/3 are excluded at 95% confidencemore » level. These are the most stringent limits to date for the considered Drell-Yan-like production mode.« less

A search is presented for the pair production of new heavy resonances, each decaying into a top quark (t) or antiquark and a gluon (g). The analysis uses data recorded with the CMS detector from proton–proton collisions at a center-of-mass energy of 13 TeV at the LHC, corresponding to an integrated luminosity of 138 fb^-1. Events with one muon or electron, multiple jets, and missing transverse momentum are selected. After using a deep neural network to enrich the data sample with signal-like events, distributions in the scalar sum of the transverse momenta of all reconstructed objects are analyzed in themore » search for a signal. No significant deviations from the standard model prediction are found. Upper limits at 95% confidence level are set on the product of cross section and branching fraction squared for the pair production of excited top quarks in the t* → tg decay channel. The upper limits range from 120 to 0.8 fb for a t* with spin-1/2 and from 15 to 1.0 fb for a t* with spin-3/2. These correspond to mass exclusion limits up to 1050 and 1700 GeV for spin-1/2 and spin-3/2 t* particles, respectively. These are the most stringent limits to date on the existence of t* → tg resonances.« less

A full set of optimized observables is measured in an angular analysis of the decay B⁰ → K* (892)⁰μ⁺μ^– using a sample of proton-proton collisions at $$\sqrt{s}$$ = 13 TeV, collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 140fb^–1. The analysis is performed in six bins of the squared invariant mass of the dimuon system, q², over the range 1.1 < q² < 16 GeV². The results are among the most precise experimental measurements of the angular observables for this decay and are compared to a variety of predictions based on the standard model.more » Some of these predictions exhibit tension with the measurements.« less

Nuclear medium effects on 𝐵⁺ meson production are studied using the binary-collision scaled cross section ratio between events of different charged-particle multiplicities from proton-lead collisions. Data, collected by the CMS experiment in 2016 at a nucleon-nucleon center-of-mass energy of $$\sqrt{𝑠_{NN}}$$ = 8.16 TeV, corresponding to an integrated luminosity of 175 nb⁻¹, were used. The scaling factors in the ratio are determined using a novel approach based on the 𝑍 → 𝜇⁻⁢𝜇⁺ cross sections measured in the same events. The scaled ratio for 𝐵⁺ is consistent with unity for all event multiplicities, putting stringent constraints on nuclear modification for heavy flavor.

A measurement of the ratio of branching fractions 𝑅⁢(𝐽/𝜓) =ℬ⁡(𝐵$$^+_𝑐$$ →𝐽/𝜓⁢𝜏⁺⁢𝜈_𝜏)/ℬ⁡(𝐵$$^+_𝑐$$ →𝐽/𝜓⁢𝜇⁺⁢𝜈_𝜇) in the 𝐽/𝜓 →𝜇⁺⁢𝜇⁻, 𝜏⁺→𝜇⁺⁢𝜈_𝜇⁢$$\bar{𝜈}$$_𝜏 decay channel is presented. This measurement uses a sample of proton-proton collision data collected at a center-of-mass energy of 13 TeV by the CMS experiment in 2018, corresponding to an integrated luminosity of 59.7 fb⁻¹. The measured ratio, 𝑅⁢(𝐽/𝜓) = 0.1⁢7$$^{+0.18}_{−0.17}⁢$$(stat)$$^{+0.21}_{−0.22⁢}$$(syst)$$^{+0.19}_{−0.18}$$⁢(theo) =0.17 ± 0.33, agrees with the value of 0.2582 ± 0.0038 predicted by the standard model, which assumes lepton flavor universality. By testing lepton flavor universality, this measurement is a probe of new physics using 𝐵$$^+_𝑐$$ mesons, which are currently only producedmore » at the LHC.« less

Measurements are presented of inclusive and differential cross sections for Z boson associated production of top quark pairs ($$ \textrm{t}\overline{\textrm{t}}\textrm{Z} $$) and single top quarks (tZq or tWZ). The data were recorded in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 138 fb$$^{−1}$$. Events with three or more leptons, electrons or muons, are selected and a multiclass deep neural network is used to separate three event categories, the $$ \textrm{t}\overline{\textrm{t}}\textrm{Z} $$ and tWZ processes, the tZq process, and the backgrounds. A profile likelihood approach is used to unfold the differential cross sections, tomore » account for systematic uncertainties, and to determine the correlations between the two signal categories in one global fit. The inclusive cross sections for a dilepton invariant mass between 70 and 110 GeV are measured to be 1.14 ± 0.07 pb for the sum of $$ \textrm{t}\overline{\textrm{t}}\textrm{Z} $$ and tWZ, and 0.81 ± 0.10 pb for tZq, in good agreement with theoretical predictions.[graphic not available: see fulltext]« less