A measurement is reported of differential top quark pair (tt) production cross sections, where top quarks are produced at large transverse momenta. The data collected with the CMS detector at the LHC ...are from pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb−1. The measurement uses events where at least one top quark decays as t → Wb → qq′b and is reconstructed as a large-radius jet with transverse momentum in excess of 400 GeV. The second top quark is required to decay either in a similar way or leptonically, as inferred from a reconstructed electron or muon, a bottom quark jet, and missing transverse momentum due to the undetected neutrino. The cross section is extracted as a function of kinematic variables of individual top quarks or of the tt system. The results are presented at the particle level, within a region of phase space close to that of the experimental acceptance, and at the parton level and are compared to various theoretical models. In both decay channels, the observed absolute cross sections are significantly lower than the predictions from theory, while the normalized differential measurements are well described.
Using a data sample of proton-proton collisions at √s = 13 TeV, corresponding to an integrated luminosity of 140 fb−1 collected by the CMS experiment in 2016–2018, the B0s → X(3872)ϕ decay is ...observed. Decays into J/ψπ+π− and K+K− are used to reconstruct, respectively, the X(3872) and ϕ. The ratio of the product of branching fractions BB0s → X(3872)ϕ BX(3872) → J/ψπ+π− to the product BB0s → ψ(2S)ϕ Bψ(2S) → J/ψπ+π− is measured to be 2.21 ± 0.29 (stat) ± 0.17 (syst) % . The ratio BB0s → X(3872)ϕ/BB0 → X(3872) K 0 is found to be consistent with one, while the ratio BB0s → X(3872)ϕ/BB+ → X(3872) K+ is two times smaller. This suggests a difference in the production dynamics of the X(3872) in B0 and B0s meson decays compared to B+. The reported observation may shed new light on the nature of the X(3872) particle.
A measurement is reported of the jet mass distribution in hadronic decays of boosted top quarks produced in pp collisions at s=13 TeV. The data were collected with the CMS detector at the LHC and ...correspond to an integrated luminosity of 35.9 fb−1. The measurement is performed in the lepton+jets channel of tt¯ events, where the lepton is an electron or muon. The products of the hadronic top quark decay t→bW→bqq¯′ are reconstructed as a single jet with transverse momentum larger than 400 GeV. The tt¯ cross section as a function of the jet mass is unfolded at the particle level and used to extract a value of the top quark mass of 172.6±2.5 GeV. A novel jet reconstruction technique is used for the first time at the LHC, which improves the precision by a factor of 3 relative to an earlier measurement. This highlights the potential of measurements using boosted top quarks, where the new technique will enable future precision measurements.
Results are presented for an extraction of the top quark Yukawa coupling from top quark-antiquark (tt¯) kinematic distributions in the lepton plus jets final state in proton-proton collisions, based ...on data collected by the CMS experiment at the LHC at √s = 13 TeV, corresponding to an integrated luminosity of 35.8 fb−1. Corrections from weak boson exchange, including Higgs bosons, between the top quarks can produce large distortions of differential distributions near the energy threshold of tt¯ production. Therefore, precise measurements of these distributions are sensitive to the Yukawa coupling. Top quark events are reconstructed with at least three jets in the final state, and a novel technique is introduced to reconstruct the tt¯ system for events with one missing jet. This technique enhances the experimental sensitivity in the low invariant mass region, Mtt¯. The data yields in Mtt¯, the rapidity difference |yt − yt¯|, and the number of reconstructed jets are compared with distributions representing different Yukawa couplings. These comparisons are used to measure the ratio of the top quark Yukawa coupling to its standard model predicted value to be 1.07−0.43+0.34 with an upper limit of 1.67 at the 95% confidence level.
Measurements of the top quark polarization and top quark pair (tt¯) spin correlations are presented using events containing two oppositely charged leptons (e+e−, e±μ∓, or μ+μ−) produced in ...proton-proton collisions at a center-of-mass energy of 13 TeV. The data were recorded by the CMS experiment at the LHC in 2016 and correspond to an integrated luminosity of 35.9 fb−1. A set of parton-level normalized differential cross sections, sensitive to each of the independent coefficients of the spin-dependent parts of the tt¯ production density matrix, is measured for the first time at 13 TeV. The measured distributions and extracted coefficients are compared with standard model predictions from simulations at next-to-leading-order (NLO) accuracy in quantum chromodynamics (QCD), and from NLO QCD calculations including electroweak corrections. All measurements are found to be consistent with the expectations of the standard model. The normalized differential cross sections are used in fits to constrain the anomalous chromomagnetic and chromoelectric dipole moments of the top quark to −0.24<CtG/Λ2<0.07 TeV−2 and −0.33 < CtGI/Λ2 < 0.20 TeV−2, respectively, at the 95% confidence level.
The modification of jet shapes in Pb-Pb collisions, relative to those in p p collisions, is studied for jets associated with an isolated photon. The data were collected with the CMS detector at the ...LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Jet shapes are constructed from charged particles with track transverse momenta (pT) above 1 GeV/c in annuli around the axes of jets with ... 30 GeV / c associated with an isolated photon with ... 60 GeV/c. The jet shape distributions are consistent between peripheral Pb-Pb and p p collisions, but are modified for more central Pb-Pb collisions. In these central Pb-Pb events, a larger fraction of the jet momentum is observed at larger distances from the jet axis compared to p p , reflecting the interaction between the partonic medium created in heavy ion collisions and the traversing partons.(ProQuest: ... denotes formulae omitted.)
The angular distribution of the flavor-changing neutral current decay B+ → K+μ+μ− is studied in proton-proton collisions at a center-of-mass energy of 8 TeV. The analysis is based on data collected ...with the CMS detector at the LHC, corresponding to an integrated luminosity of 20.5 fb−1. The forward-backward asymmetry AFB of the dimuon system and the contribution FH from the pseudoscalar, scalar, and tensor amplitudes to the decay width are measured as a function of the dimuon mass squared. The measurements are consistent with the standard model expectations.
A measurement of jet substructure observables is presented using tt¯ events in the lepton+jets channel from proton-proton collisions at s=13 TeV recorded by the CMS experiment at the LHC, ...corresponding to an integrated luminosity of 35.9 fb−1. Multiple jet substructure observables are measured for jets identified as bottom, light-quark, and gluon jets, as well as for inclusive jets (no flavor information). The results are unfolded to the particle level and compared to next-to-leading-order predictions from powheg interfaced with the parton shower generators pythia 8 and herwig 7, as well as from sherpa 2 and Dire 2. A value of the strong coupling at the Z boson mass, αS(mZ)=0.115−0.013+0.015, is extracted from the substructure data at leading-order plus leading-log accuracy.
This Letter presents the observation of the rare Z boson decay Z→ψℓ+ℓ−. Here, ψ represents contributions from direct J/ψ and ψ(2S)→J/ψX, ℓ+ℓ− is a pair of electrons or muons, and the J/ψ meson is ...detected via its decay to μ+μ−. The sample of proton-proton collision data, collected by the CMS experiment at the LHC at a center-of-mass energy of 13 TeV, corresponds to an integrated luminosity of 35.9 fb−1. The signal is observed with a significance in excess of 5 standard deviations. After subtraction of the ψ(2S)→J/ψX contribution, the ratio of the branching fraction of the exclusive decay Z→J/ψℓ+ℓ− to the decay Z→μ+μ−μ+μ− within a fiducial phase space is measured to be B(Z→J/ψℓ+ℓ−)/B(Z→μ+μ−μ+μ−)=0.67±0.18(stat)±0.05(syst).
Differential and double-differential cross sections for the production of top quark pairs in proton-proton collisions at s=13 TeV are measured as a function of kinematic variables of the top quarks ...and the top quark-antiquark (tt¯) system. In addition, kinematic variables and multiplicities of jets associated with the tt¯ production are measured. This analysis is based on data collected by the CMS experiment at the LHC in 2016 corresponding to an integrated luminosity of 35.8 fb−1. The measurements are performed in the lepton+jets decay channels with a single muon or electron and jets in the final state. The differential cross sections are presented at the particle level, within a phase space close to the experimental acceptance, and at the parton level in the full phase space. The results are compared to several standard model predictions that use different methods and approximations. The kinematic variables of the top quarks and the tt¯ system are reasonably described in general, though none predict all the measured distributions. In particular, the transverse momentum distribution of the top quarks is more steeply falling than predicted. The kinematic distributions and multiplicities of jets are adequately modeled by certain combinations of next-to-leading-order calculations and parton shower models.
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