The polarizations of prompt and non-prompt J$/\psi$ and $\psi$(2S) mesons are measured in proton-proton collisions at $\sqrt{s}$ = 13 TeV, using data samples collected by the CMS experiment in 2017 and 2018, corresponding to a total integrated luminosity of 103.3 fb$^{-1}$. Based on the analysis of the dimuon decay angular distributions in the helicity frame, the polar anisotropy, $\lambda_\theta$, is measured as a function of the transverse momentum, $p_\mathrm{T}$, of the charmonium states, in the 25-120 and 20-100 GeV ranges for the J$/\psi$ and $\psi$(2S), respectively. The non-prompt polarizations agree with predictions based on the hypothesis that, for $p_\mathrm{T}$$\gtrsim$ 25 GeV, the non-prompt J$/\psi$ and $\psi$(2S) are predominantly produced in two-body B meson decays. The prompt results clearly exclude strong transverse polarizations, even for $p_\mathrm{T}$ exceeding 30 times the J$/\psi$ mass, where $\lambda_\theta$ tends to an asymptotic value around 0.3. Taken together with previous measurements, by CMS and LHCb at $\sqrt{s}$ = 7 TeV, the prompt polarizations show a significant variation with $p_\mathrm{T}$, at low $p_\mathrm{T}$.
prompt $\mathrm{J}\mspace{-2mu}/\mspace{-2mu}\psi$ $\lambda_\theta$
non prompt $\mathrm{J}\mspace{-2mu}/\mspace{-2mu}\psi$ $\lambda_\theta$
prompt $\psi(2S)$ $\lambda_\theta$
The production cross sections of the B+, B0, and B0s mesons, and of their charge conjugates, are measured via exclusive hadronic decays in pPb collisions at the center-of-mass energy sqrt(s_NN) = 5.02 TeV with the CMS detector at the CERN LHC. The data set used for this analysis corresponds to an integrated luminosity of 34.6 inverse nanobarns. The production cross sections are measured in the transverse momentum range between 10 and 60 GeV/c. No significant modification is observed compared to proton-proton perturbative QCD calculations scaled by the number of incoherent nucleon-nucleon collisions. These results provide a baseline for the study of in-medium b quark energy loss in PbPb collisions.
The measured $p_{\rm{T}}$-differential production cross section of $B^{+}$ in $p$ + Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV, together with the cross section calculated by the FONLL model.
The measured $p_{\rm{T}}$-differential production cross section of $B^{0}$ in $p$ + Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV, together with the cross section calculated by the FONLL model.
The measured $p_{\rm{T}}$-differential production cross section of $B_{s}^{0}$ in $p$ + Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV, together with the cross section calculated by the FONLL model.
The production of jets associated to bottom quarks is measured for the first time in PbPb collisions at a center-of-mass energy of 2.76 TeV per nucleon pair. Jet spectra are reported in the transverse momentum (pt) range of 80-250 GeV, and within pseudorapidity abs(eta < 2). The nuclear modification factor (R[AA]) calculated from these spectra shows a strong suppression in the b-jet yield in PbPb collisions relative to the yield observed in pp collisions at the same energy. The suppression persists to the largest values of pt studied, and is centrality dependent. The R[AA] is about 0.4 in the most central events, similar to previous observations for inclusive jets. This implies that jet quenching does not have a strong dependence on parton mass and flavor in the jet pt range studied.
The b-jet yield as a function of pT is for the 0-100% centrality class of PbPb collisions. The yields are scaled by the equivalent number of minimum bias events sampled and by TAA.
The b-jet yield as a function of pT is for the 0-10% centrality class of PbPb collisions. The yields are scaled by the equivalent number of minimum bias events sampled and by TAA.
The b-jet yield as a function of pT is for the 10-30% centrality class of PbPb collisions. The yields are scaled by the equivalent number of minimum bias events sampled and by TAA.
We present a measurement of b jet transverse momentum (pt) spectra in proton-lead (pPb) collisions using a dataset corresponding to about 35 inverse nanobarns collected with the CMS detector at the LHC. Jets from b quark fragmentation are found by exploiting the long lifetime of hadrons containing a b quark through tagging methods using distributions of the secondary vertex mass and displacement. Extracted cross sections for b jets are scaled by the effective number of nucleon-nucleon collisions and are compared to a reference obtained from PYTHIA simulations of pp collisions. The PYTHIA-based estimate of the nuclear modification factor is found to be 1.22 +/- 0.15 (stat + syst pPb) +/- 0.27 (syst PYTHIA) averaged over all jets with pt between 55 and 400 GeV/c and with abs(eta[lab]) < 2. We also compare this result to predictions from models using perturbative calculations in quantum chromodynamics.
Distributions of the b-tagging efficiency as a function of the mistag rate of light jets for pp collisions in a PYTHIA simulation.
Distributions of the b-tagging efficiency as a function of the mistag rate of charm jets for pp collisions in a PYTHIA simulation.
Distributions of the b-tagging efficiency as a function of the mistag rate of light jets for pPb collisions in a PYTHIA+HIJING simulation.
The production of Z bosons in pPb collisions at sqrt(s[NN]) = 5.02 TeV is studied by the CMS experiment via the electron and muon decay channels. The inclusive cross section is compared to pp collision predictions, and found to scale with the number of elementary nucleon-nucleon collisions. The differential cross sections as a function of the Z boson rapidity and transverse momentum are measured. Though they are found to be consistent within uncertainty with theoretical predictions both with and without nuclear effects, the forward-backward asymmetry suggests the presence of nuclear effects at large rapidities. These results provide new data for constraining nuclear parton distribution functions.
Differential cross section of the Z bosons in pPb collisions as a function of rapidity in the fiducial region for the combined leptonic decay channel.
Forward-backward asymmetry (AFB) distribution of the Z bosons in pPb collisions as a function of rapidity in the fiducial region for the combined leptonic decay channel.
Differential cross section of the Z bosons in pPb collisions as a function of transverse momentum in the fiducial region for the combined leptonic decay channel.
The production of Z bosons is studied in the dimuon and dielectron decay channels in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV, using data collected by the CMS experiment at the LHC. The PbPb data sample corresponds to an integrated luminosity of about 150 inverse microbarns, while the pp data sample collected in 2013 at the same nucleon-nucleon centre-of-mass energy has an integrated luminosity of 5.4 inverse picobarns. The Z boson yield is measured as a function of rapidity, transverse momentum, and collision centrality. The ratio of PbPb to pp yields, scaled by the number of inelastic nucleon-nucleon collisions, is found to be 1.06 +/- 0.05 (stat) +/- 0.08 (syst) in the dimuon channel and 1.02 +/- 0.08 (stat) +/- 0.15 (syst) in the dielectron channel, for centrality-integrated Z boson production. This binary collision scaling is seen to hold in the entire kinematic region studied, as expected for a colourless probe that is unaffected by the hot and dense QCD medium produced in heavy ion collisions.
The measured Z boson production cross section in pp collisions as a function of the Z boson pT for the dimuon decay channel in |y|<2.0.
The measured Z boson production cross section in pp collisions as a function of the Z boson pT for the dielectron decay channel in |y|<1.44.
The measured Z boson production cross section in pp collisions as a function of the Z boson rapidity for the dimuon decay channel.
The $B_\mathrm{c}^+$ meson is observed for the first time in heavy ion collisions. Data from the CMS detector are used to study the production of the $B_\mathrm{c}^+$ meson in lead-lead (PbPb) and proton-proton (pp) collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\mathrm{NN}}} =$ 5.02 TeV, via the $B_\mathrm{c}^+ \to (J/\psi\to\mu^+\mu^-)\mu^+\nu_\mu$ decay. The $B_\mathrm{c}^+$ nuclear modification factor, derived from the PbPb-to-pp ratio of production cross sections, is measured in two bins of the trimuon transverse momentum and of the PbPb collision centrality. The B$_\mathrm{c}^+$ meson is shown to be less suppressed than quarkonia and most of the open heavy-flavor mesons, suggesting that effects of the hot and dense nuclear matter created in heavy ion collisions contribute to its production. This measurement sets forth a promising new probe of the interplay of suppression and enhancement mechanisms in the production of heavy-flavor mesons in the quark-gluon plasma.
The $B_c$ meson production (pp-equivalent) cross-section times branching fraction of the $B_c\rightarrow (J/\psi \rightarrow \mu\mu) \mu \nu_{\mu}$ decay in pp and PbPb collisions. The used kinematic variables correspond to those of the trimuon final state. The two $p_T$ bins correspond to different rapidity ranges. The total uncertainty is decomposed in an uncertainty from the fit and one representing all other sources. The markers of the $p_T^{\mu\mu\mu}$ bins are placed according to the Lafferty-Wyatt prescription.
The $B_c$ meson nuclear modification factor in PbPb collisions, in $p_T^{\mu\mu\mu}$ bins corresponding to different trimuon rapidity ranges. The total uncertainty is decomposed in a bin-to-bin-uncorrelated uncertainty and one fully correlated along the two bins. The markers of the $p_T^{\mu\mu\mu}$ bins are placed at the average of the Lafferty-Wyatt prescriptions applied to the pp and PbPb spectra.
The $B_c$ meson nuclear modification factor in PbPb collisions, in centrality bins, integrated over the studied kinematic range. The cut on the trimuon rapidity depends on the trimuon $p_T$. The total uncertainty is decomposed in a bin-to-bin-uncorrelated uncertainty and one fully correlated along the two bins. The centrality bin markers are placed at the minimum bias average number of participants $N_{part}$.
Spectra of identified charged hadrons are measured in pPb collisions with the CMS detector at the LHC at sqrt(sNN) = 5.02 TeV. Charged pions, kaons, and protons in the transverse-momentum range pt approximately 0.1-1.7 GeV and laboratory rapidity abs(y) < 1 are identified via their energy loss in the silicon tracker. The average pt increases with particle mass and the charged multiplicity of the event. The increase of the average pt with charged multiplicity is greater for heavier hadrons. Comparisons to Monte Carlo event generators reveal that EPOS LHC, which incorporates additional hydrodynamic evolution of the created system, is able to reproduce most of the data features, unlike HIJING and AMPT. The pt spectra and integrated yields are also compared to those measured in pp and PbPb collisions at various energies. The average transverse momentum and particle ratio measurements indicate that particle production at LHC energies is strongly correlated with event particle multiplicity.
.
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.
Correlation matrix for the systematic uncertainties, excluding integrated luminosity, as a function of $p_{\textrm{T}}$ for $15<m_{\mu\mu}<60$ GeV.
The normalized differential cross section for top quark pair (tt-bar) production is measured in pp collisions at a centre-of-mass energy of 8 TeV at the CERN LHC using the CMS detector in data corresponding to an integrated luminosity of 19.7 inverse femtobarns. The measurements are performed in the lepton + jets (e/mu + jets) and in the dilepton (e+e-, mu+mu-, and e+-mu-+) decay channels. The tt-bar cross section is measured as a function of the kinematic properties of the charged leptons, the jets associated to b quarks, the top quarks, and the tt-bar system. The data are compared with several predictions from perturbative quantum chromodynamics up to approximate next-to-next-to-leading-order precision. No significant deviations are observed relative to the standard model predictions.
Statistical covariance matrix for the normalized differential tt cross section (from l+jets channel) as a function of the rapidity y of the top quark or antiquark.