Explore the vast range of titles available.

We present the first study of charged-hadron production associated with jets originating from b quarks in proton-proton collisions at a center-of-mass energy of 5.02 TeV. The data sample used in this study was collected with the CMS detector at the CERN LHC and corresponds to an integrated luminosity of 27.4 pb-1. To characterize the jet substructure, the differential jet shapes, defined as the normalized transverse momentum distribution of charged hadrons as a function of angular distance from the jet axis, are measured for b jets. In addition to the jet shapes, the per-jet yields of charged particles associated with b jets are also quantified, again as a function of the angular distance with respect to the jet axis. Extracted jet shape and particle yield distributions for b jets are compared with results for inclusive jets, as well as with the predictions from the pythia and herwig++ event generators.

Measurements of the cross section for the production of top quark pairs in association with a pair of jets from bottom quarks$$ \\left({\\sigma}_{\\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{b}\\overline{\\mathrm{b}}}\\right) $$σ t t ¯ b b ¯ and in association with a pair of jets from quarks of any flavor or gluons$$ \\left({\\sigma}_{\\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{jj}}\\right) $$σ t t ¯ jj and their ratio are presented. The data were collected in proton-proton collisions at a center-of-mass energy of 13 TeV by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of 35.9 fb − 1 . The measurements are performed in a fiducial phase space and extrapolated to the full phase space, separately for the dilepton and lepton+jets channels, where lepton corresponds to either an electron or a muon. The results of the measurements in the fiducial phase space for the dilepton and lepton+jets channels, respectively, are$$ {\\sigma}_{\\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{jj}} $$σ t t ¯ jj = 2 . 36 ± 0 . 02 (stat) ± 0 . 20 (syst) pb and 31 . 0 ± 0 . 2 (stat) ± 2 . 9 (syst) pb, and for the cross section ratio 0 . 017 ± 0 . 001 (stat) ± 0 . 001 (syst) and 0 . 020 ± 0 . 001 (stat) ± 0 . 001 (syst). The values of$$ {\\sigma}_{\\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{b}\\overline{\\mathrm{b}}} $$σ t t ¯ b b ¯ are determined from the product of the$$ {\\sigma}_{\\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{jj}} $$σ t t ¯ jj and the cross section ratio, obtaining, respectively, 0 . 040 ± 0 . 002 (stat) ± 0 . 005 (syst) pb and 0 . 62 ± 0 . 03 (stat) ± 0 . 07 (syst) pb. These measurements are the most precise to date and are consistent, within the uncertainties, with the standard model expectations obtained using a matrix element calculation at next-to-leading order in quantum chromodynamics matched to a parton shower.

Twelve measurements of inclusive cross sections of W ± and Z boson production, performed in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, are compared with perturbative quantum chromodynamics calculations at next-to-next- to-leading order (NNLO) accuracy obtained with the CT14, HERAPDF2.0, MMHT14, and NNPDF3.0 parton distribution functions (PDFs). Data and theory agree well for all PDF sets, taking into account the experimental and theoretical uncertainties. A novel procedure is employed to extract the strong coupling constant at the Z pole mass from a detailed comparison of all the experimental fiducial cross sections to the corresponding NNLO theoretical predictions, yielding$$ {\\alpha}_{\\mathrm{S}}\\left({m}_{\\mathrm{Z}}\\right)={0.1163}_{-0.0031}^{+0.0024} $$α S m Z = 0.1163 − 0.0031 + 0.0024 (CT14),$$ {0.1072}_{-0.0040}^{+0.0043} $$0.1072 − 0.0040 + 0.0043 (HERAPDF2.0), 0 . 1186 ± 0 . 0025 (MMHT14), and 0.1147 ± 0.0023 (NNPDF3.0). Using the results obtained with the CT14 and MMHT14 PDFs, which yield the most robust and stable α S ( m Z ) extractions, a value$$ {\\alpha}_{\\mathrm{S}}\\left({m}_{\\mathrm{Z}}\\right)={0.1175}_{-0.0028}^{+0.0025} $$α S m Z = 0.1175 − 0.0028 + 0.0025 is determined.

The parton-level top quark (t) forward-backward asymmetry and the anomalous chromoelectric (dᵗ) and chromomagnetic (μᵗ) moments have been measured using LHC pp collisions at a center-of-mass energy of 13 TeV, collected in the CMS detector in a data sample corresponding to an integrated luminosity of 35.9 fb–1. The linearized variable A ⁽¹⁾_(FB) is used to approximate the asymmetry. Candidate tt¯ events decaying to a muon or electron and jets in final states with low and high Lorentz boosts are selected and reconstructed using a fit of the kinematic distributions of the decay products to those expected for tt¯ final states. The values found for the parameters are A ⁽¹⁾_(FB) = 0.048 ^(+0.095)_(–0.087) (stat) ^(+0.020)_(–0.029) (syst), μᵗ = –0.024 ^(+0.013)_(–0.009) (stat) ^(+0.016)_(–0.011) (syst), and a limit is placed on the magnitude of ∥dᵗ∥ < 0.03 at 95% confidence level.

A data sample of events from proton-proton collisions with at least two jets, and two isolated same-sign or three or more charged leptons, is studied in a search for signatures of new physics phenomena. The data correspond to an integrated luminosity of$$137{\\,{\\text {fb}}^{-1}} $$137 fb - 1 at a center-of-mass energy of$$13\\,{\\text {TeV}} $$13 TeV , collected in 2016–2018 by the CMS experiment at the LHC. The search is performed using a total of 168 signal regions defined using several kinematic variables. The properties of the events are found to be consistent with the expectations from standard model processes. Exclusion limits at 95% confidence level are set on cross sections for the pair production of gluinos or squarks for various decay scenarios in the context of supersymmetric models conserving or violating R parity. The observed lower mass limits are as large as$$2.1\\,{\\text {TeV}} $$2.1 TeV for gluinos and$$0.9\\,{\\text {TeV}} $$0.9 TeV for top and bottom squarks. To facilitate reinterpretations, model-independent limits are provided in a set of simplified signal regions.

Results are presented from a search for events containing an excited lepton (electron or muon) produced in association with an ordinary lepton of the same flavor and decaying to a lepton and two hadronic jets. Both the production and the decay of the excited leptons are assumed to occur via a contact interaction with a characteristic energy scale Λ. The branching fraction for the decay mode under study increases with the mass of the excited lepton and is the most sensitive channel for very heavy excited leptons. The analysis uses a sample of proton-proton collisions collected by the CMS experiment at the LHC at$$ \\sqrt{s} $$s = 13 TeV, corresponding to an integrated luminosity of 77.4 fb − 1 . The four-body invariant mass of the two lepton plus two jet system is used as the primary discriminating variable. No significant excess of events beyond the expectation for standard model processes is observed. Assuming that Λ is equal to the mass of the excited leptons, excited electrons and muons with masses below 5.6 and 5.7 TeV, respectively, are excluded at 95% confidence level. These are the best limits to date.

Results are reported for the$$ {\\mathrm{B}}_{\\mathrm{s}}^0 $$B s 0 → μ + μ − branching fraction and effective lifetime and from a search for the decay B 0 → μ + μ − . The analysis uses a data sample of proton-proton collisions accumulated by the CMS experiment in 2011, 2012, and 2016, with center-of-mass energies (integrated luminosities) of 7 TeV (5 fb − 1 ), 8 TeV (20 fb − 1 ), and 13 TeV (36 fb − 1 ). The branching fractions are determined by measuring event yields relative to B + → J / ψK + decays (with J / ψ → μ + μ − ), which results in the reduction of many of the systematic uncertainties. The decay$$ {\\mathrm{B}}_{\\mathrm{s}}^0 $$B s 0 → μ + μ − is observed with a significance of 5.6 standard deviations. The branching fraction is measured to be$$ \\mathrm{\\mathcal{B}}\\left({\\mathrm{B}}_{\\mathrm{s}}^0\\to {\\upmu}^{+}{\\upmu}^{-}\\right)=\\left[2.9\\pm 0.7\\left(\\exp \\right)\\pm 0.2\\left(\\mathrm{frag}\\right)\\right]\\times {10}^{-9} $$ℬ B s 0 → μ + μ − = 2.9 ± 0.7 exp ± 0.2 frag × 10 − 9 , where the first uncertainty combines the experimental statistical and systematic contributions, and the second is due to the uncertainty in the ratio of the$$ {\\mathrm{B}}_{\\mathrm{s}}^0 $$B s 0 and the B + fragmentation functions. No significant excess is observed for the decay B 0 → μ + μ − , and an upper limit of ℬ(B 0  → μ + μ − ) < 3.6 × 10 −10 is obtained at 95% confidence level. The$$ {\\mathrm{B}}_{\\mathrm{s}}^0 $$B s 0 → μ+μ − effective lifetime is measured to be$$ {\\tau}_{\\upmu^{+}{\\upmu}^{-}}={1.70}_{-0.44}^{+0.61} $$τ μ + μ − = 1.70 − 0.44 + 0.61 ps. These results are consistent with standard model predictions.

A measurement of the inclusive cross section of top quark pair production in association with a Z boson using proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC is performed. The data sample corresponds to an integrated luminosity of 77.5 fb-1, collected by the CMS experiment during 2016 and 2017. The measurement is performed using final states containing three or four charged leptons (electrons or muons), and the Z boson is detected through its decay to an oppositely charged lepton pair. The production cross section is measured to be σ( \\( \\mathrm{t}\\overline{\\mathrm{t}}\\mathrm{Z} \\) ) = 0.95 ± 0.05 (stat) ± 0.06 (syst) pb. For the first time, differential cross sections are measured as functions of the transverse momentum of the Z boson and the angular distribution of the negatively charged lepton from the Z boson decay. The most stringent direct limits to date on the anomalous couplings of the top quark to the Z boson are presented, including constraints on the Wilson coefficients in the framework of the standard model effective field theory.

A search for physics beyond the standard model in events with at least three charged leptons (electrons or muons) is presented. The data sample corresponds to an integrated luminosity of 137 fb-1 of proton-proton collisions at √s̅ = 13 TeV, collected with the CMS detector at the LHC in 2016-2018. The two targeted signal processes are pair production of type-III seesaw heavy fermions and production of a light scalar or pseudoscalar boson in association with a pair of top quarks. The heavy fermions may be manifested as an excess of events with large values of leptonic transverse momenta or missing transverse momentum. The light scalars or pseudoscalars may create a localized excess in the dilepton mass spectra. The results exclude heavy fermions of the type-III seesaw model for masses below 880 GeV at 95% confidence level in the scenario of equal branching fractions to each lepton flavor. This is the most restrictive limit on the flavor-democratic scenario of the type-III seesaw model to date. Assuming a Yukawa coupling of unit strength to top quarks, branching fractions of new scalar (pseudoscalar) bosons to dielectrons or dimuons above 0.004 (0.03) and 0.04 (0.03) are excluded at 95% confidence level for masses in the range 15-75 and 108-340 GeV, respectively. These are the first limits in these channels on an extension of the standard model with scalar or pseudoscalar particles.