The production cross sections for prompt open-charm mesons in proton-proton collisions at a center-of-mass energy of 13 TeV are reported. The measurement is performed using a data sample collected by the CMS experiment corresponding to an integrated luminosity of 29 nb$^{-1}$. The differential production cross sections of the D$^{*\pm}$, D$^\pm$, and D$^0$ ($\overline{\mathrm{D}}^{0}$) mesons are presented in ranges of transverse momentum and pseudorapidity 4 $\lt$$p_\mathrm{T}$$\lt$ 100 GeV and $\lvert\eta\rvert$$\lt$ 2.1, respectively. The results are compared to several theoretical calculations and to previous measurements.
Measurements are presented of the differential cross sections for Z bosons produced in proton-proton collisions at $\sqrt{s} =$ 13 TeV and decaying to muons and electrons. The data analyzed were collected in 2016 with the CMS detector at the LHC and correspond to an integrated luminosity of 35.9 fb$^{-1}$. The measured fiducial inclusive product of cross section and branching fraction agrees with next-to-next-to-leading order quantum chromodynamics calculations. Differential cross sections of the transverse momentum $p_\mathrm{T}$, the optimized angular variable $\phi^*_\eta$, and the rapidity of lepton pairs are measured. The data are corrected for detector effects and compared to theoretical predictions using fixed order, resummed, and parton shower calculations. The uncertainties of the measured normalized cross sections are smaller than 0.5% for $\phi^*_\eta <$ 0.5 and for $p_\mathrm{T}^\mathrm{Z} <$ 50 GeV.
The transverse energy ($E_\mathrm{T}^{\gamma}$) spectra of photons isolated from other particles are measured using proton-proton (pp) and lead-lead (PbPb) collisions at the LHC at $\sqrt{s_\mathrm{NN}} =$ 5.02 TeV with integrated luminosities of 27.4 pb$^{-1}$and 404 $\mu$b$^{-1}$ for pp and PbPb data, respectively. The results are presented for photons with 25 $<$ $E_\mathrm{T}^{\gamma}$ $<$ 200 GeV in the pseudorapidity range $|\eta|$ $<$ 1.44, and for different centrality intervals for PbPb collisions. Photon production in PbPb collisions is consistent with that in pp collisions scaled by the number of binary nucleon-nucleon collisions, demonstrating that photons do not interact with the quark-gluon plasma. Therefore, isolated photons can provide information about the initial energy of the associated parton in photon+jet measurements. The results are compared with predictions from the next-to-leading-order JETPHOX generator for different parton distribution functions (PDFs) and nuclear PDFs (nPDFs). The comparisons can help to constrain the nPDFs global fits.
Differential cross sections for the Drell-Yan process, including Z boson production, using the dimuon decay channel are measured in proton-lead (pPb) collisions at a nucleon-nucleon centre-of-mass energy of 8.16 TeV. A data sample recorded with the CMS detector at the LHC is used, corresponding to an integrated luminosity of 173 nb$^{-1}$. The differential cross section as a function of the dimuon mass is measured in the range 15-600 GeV, for the first time in proton-nucleus collisions. It is also reported as a function of dimuon rapidity over the mass ranges 15-60 GeV and 60-120 GeV, and ratios for the p-going over the Pb-going beam directions are built. In both mass ranges, the differential cross sections as functions of the dimuon transverse momentum $p_\mathrm{T}$ and of a geometric variable $\phi^*$ are measured, where $\phi^*$ highly correlates with $p_\mathrm{T}$ but is determined with higher precision. In the Z mass region, the rapidity dependence of the data indicate a modification of the distribution of partons within a lead nucleus as compared to the proton case. The data are more precise than predictions based upon current models of parton distributions.
Measurements of the second Fourier harmonic coefficient ($v_2$) of the azimuthal distributions of prompt and nonprompt D$^0$ mesons produced in pp and pPb collisions are presented. Nonprompt D$^0$ mesons come from beauty hadron decays. The data samples are collected by the CMS experiment at nucleon-nucleon center-of-mass energies of 13 and 8.16 TeV, respectively. In high multiplicity pp collisions, $v_2$ signals for prompt charm hadrons are reported for the first time, and are found to be comparable to those for light-flavor hadron species over a transverse momentum ($p_\mathrm{T}$) range of 2-6 GeV. Compared at similar event multiplicities, the prompt D$^0$ meson $v_2$ values in pp and pPb collisions are similar in magnitude. The $v_2$ values for open beauty hadrons are extracted for the first time via nonprompt D$^0$ mesons in pPb collisions. For $p_\mathrm{T}$ in the range of 2-5 GeV, the results suggest that $v_2$ for nonprompt D$^0$ mesons are smaller than those for prompt D$^0$ mesons. These new measurements indicate a positive charm hadron $v_2$ in pp collisions and suggest a mass dependence in $v_2$ between charm and beauty hadrons in the pPb system. These results provide insights into the origin of heavy-flavor quark collectivity in small systems.
A search is presented for the associated production of a Higgs boson with a top quark pair in the all-jet final state. Events containing seven or more jets are selected from a sample of proton-proton collisions at $\sqrt{s} =$ 13 TeV collected with the CMS detector at the LHC in 2016, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. To separate the $\mathrm{t}\overline{\mathrm{t}}$H signal from the irreducible $\mathrm{t}\overline{\mathrm{t}}+\mathrm{b}\overline{\mathrm{b}}$ background, the analysis assigns leading order matrix element signal and background probability densities to each event. A likelihood-ratio statistic based on these probability densities is used to extract the signal. The results are provided in terms of an observed $\mathrm{t}\overline{\mathrm{t}}$H signal strength relative to the standard model production cross section $\mu=\sigma/\sigma_\mathrm{SM}$, assuming a Higgs boson mass of 125 GeV. The best fit value is $\hat{\mu} =$ 0.9 $\pm$ 0.7 (stat) $\pm$ 1.3 (syst) = 0.9 $\pm$ 1.5 (tot), and the observed and expected upper limits are, respectively, $\mu <$ 3.8 and $<$ 3.1 at 95% confidence levels.
A measurement is presented of the associated production of a single top quark and a W boson in proton-proton collisions at $\sqrt{s}=$ 13 TeV by the CMS Collaboration at the CERN LHC. The data collected corresponds to an integrated luminosity of 35.9 fb$^{-1}$. The measurement is performed using events with one electron and one muon in the final state along with at least one jet originated from a bottom quark. A multivariate discriminant, exploiting the kinematic properties of the events, is used to separate the signal from the dominant $\mathrm{t\overline{t}}$ background. The measured cross section of 63.1 $\pm$ 1.8 (stat) $\pm$ 6.4 (syst) $\pm$ 2.1 (lumi) pb is in agreement with the standard model expectation.
A search for Higgs bosons that decay into a bottom quark-antiquark pair and are accompanied by at least one additional bottom quark is performed with the CMS detector. The data analyzed were recorded in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} =$ 13 TeV at the LHC, corresponding to an integrated luminosity of 35.7 fb$^{-1}$. The final state considered in this analysis is particularly sensitive to signatures of a Higgs sector beyond the standard model, as predicted in the generic class of two Higgs doublet models (2HDMs). No signal above the standard model background expectation is observed. Stringent upper limits on the cross section times branching fraction are set for Higgs bosons with masses up to 1300 GeV. The results are interpreted within several MSSM and 2HDM scenarios.
A measurement for inclusive 2- and 3-jet events of the azimuthal correlation between the two jets with the largest transverse momenta, $\Delta\phi_{12}$ , is presented. The measurement considers events where the two leading jets are nearly collinear ("back-to-back") in the transverse plane and is performed for several ranges of the leading jet transverse momentum. Proton-proton collision data collected with the CMS experiment at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 35.9 fb$^{-1}$ are used. Predictions based on calculations using matrix elements at leading-order and next-to-leading-order accuracy in perturbative quantum chromodynamics supplemented with leading-log parton showers and hadronization are generally in agreement with the measurements. Discrepancies between the measurement and theoretical predictions are as large as 15%, mainly in the region 177$^\circ$ $<$ $\Delta\phi_{12}$ $<$ 180$^\circ$. The 2- and 3-jet measurements are not simultaneously described by any of models.
The associated production of a W and a Z boson is studied in final states with multiple leptons produced in proton-proton (pp) collisions at a centre-of-mass energy of 13 TeV using 137 fb$^{-1}$ of data collected with the CMS detector at the LHC. A measurement of the total inclusive production cross section yields $\sigma_{\text{tot}}$(pp $\to$ WZ) = 50.6 $\pm$ 0.8 (stat) $\pm$ 1.5 (syst) $\pm$ 1.1 (lumi) $\pm$ 0.5 (theo) pb. Measurements of the fiducial and differential cross sections for several key observables are also performed in all the final-state lepton flavour and charge compositions with a total of three charged leptons, which can be electrons or muons. All results are compared with theoretical predictions computed up to next-to-next-to-leading order in quantum chromodynamics plus next-to-leading order in electroweak theory and for various sets of parton distribution functions. The results include direct measurements of the charge asymmetry and the W and Z vector boson polarization. The first observation of longitudinally polarized W bosons in WZ production is reported. Anomalous gauge couplings are searched for, leading to new constraints on beyond-the-standard-model contributions to the WZ triple gauge coupling.
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