229 Search Results

The first measurements of the Fourier coefficients ( $V_{n\mathrm{\Delta }}$ ) of the azimuthal distributions of charged hadrons emitted from photon-proton (γp) interactions are presented. The data are extracted from 68.8 nb⁻¹ of ultra-peripheral proton-lead (pPb) collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=8.16\text{TeV}$ using the CMS detector. The high energy lead ions produce a flux of photons that can interact with the oncoming proton. This γp system provides a set of uniquemore » initial conditions with multiplicity lower than in photon-lead collisions but comparable to recent electron-positron and electron-proton data. The $V_{n\mathrm{\Delta }}$ coefficients are presented in ranges of event multiplicity and transverse momentum ( $p_{\mathrm{T}}$ ) and are compared to corresponding hadronic minimum bias pPb results. For a given multiplicity range, the mean $p_{\mathrm{T}}$ of charged particles is smaller in γp than in pPb collisions. For both the γp and pPb samples, $V_{1\mathrm{\Delta }}$ is negative, $V_{2\mathrm{\Delta }}$ is positive, and $V_{3\mathrm{\Delta }}$ consistent with 0. For each multiplicity and $p_{\mathrm{T}}$ range, $V_{2\mathrm{\Delta }}$ is larger for γp events. The γp data are consistent with model predictions that have no collective effects.« less

Results are presented from a search for CP violation in top quark pair production, using proton-proton collisions at a center-of-mass energy of 13 TeV. The data used for this analysis consist of final states with two charged leptons collected by the CMS experiment, and correspond to an integrated luminosity of 35.9 fb$$^{−1}$$. The search uses two observables, $$ \mathcal{O} _{1}$$ and $$ \mathcal{O} _{3}$$, which are Lorentz scalars. The observable $$ \mathcal{O} _{1}$$ is constructed from the four-momenta of the charged leptons and the reconstructed top quarks, while $$ \mathcal{O} _{3}$$ consists of the four-momenta of the charged leptons andmore » the b quarks originating from the top quarks. Asymmetries in these observables are sensitive to CP violation, and their measurement is used to determine the chromoelectric dipole moment of the top quark. The results are consistent with the expectation from the standard model.[graphic not available: see fulltext]« less

Production cross sections of Image 1, Image 2, and Image 3 states decaying into Image 4 in proton-lead ( $\mathrm{p}\mathrm{Pb}$ ) collisions are reported using data collected by the CMS experiment at $\sqrt{s_{{}_{\mathrm{NN}}}}=5.02\text{TeV}$ . A comparison is made with corresponding cross sections obtained with $\mathrm{p}\mathrm{p}$ data measured at the same collision energy and scaled by the Pb nucleus mass number. The nuclear modification factor for Image 1 ismore » found to be Image 5. Similar results for the excited states indicate a sequential suppression pattern, such that Image 6. The suppression of all states is much less pronounced in $\mathrm{p}\mathrm{Pb}$ than in PbPb collisions, and independent of transverse momentum Image 7 and center-of-mass rapidity Image 8 of the individual Image 9 state in the studied range Image 10 and Image 11. Models that incorporate final-state effects of bottomonia in pPb collisions are in better agreement with the data than those which only assume initial-state modifications.« less

Jet production in lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV is studied with the CMS detector at the LHC, using PbPb and pp data samples corresponding to integrated luminosities of 404 μb$$^{−1}$$ and 27.4 pb$$^{−1}$$, respectively. Jets with different areas are reconstructed using the anti-k$$_{T}$$ algorithm by varying the distance parameter R. The measurements are performed using jets with transverse momenta (p$$_{T}$$) greater than 200 GeV and in a pseudorapidity range of |η| < 2. To reveal the medium modification of the jet spectra in PbPb collisions, the properly normalized ratio of spectramore » from PbPb and pp data is used to extract jet nuclear modification factors as functions of the PbPb collision centrality, p$$_{T}$$ and, for the first time, as a function of R up to 1.0. For the most central collisions, a strong suppression is observed for high-p$$_{T}$$ jets reconstructed with all distance parameters, implying that a significant amount of jet energy is scattered to large angles. The dependence of jet suppression on R is expected to be sensitive to both the jet energy loss mechanism and the medium response, and so the data are compared to several modern event generators and analytic calculations. The models considered do not fully reproduce the data.[graphic not available: see fulltext]« less

Measurements of the differential cross sections of Z + jets and γ + jets production, and their ratio, are presented as a function of the boson transverse momentum. Measurements are also presented of the angular distribution between the Z boson and the closest jet. The analysis is based on pp collisions at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 35.9 fb$$^{−1}$$ recorded by the CMS experiment at the LHC. The results, corrected for detector effects, are compared with various theoretical predictions. In general, the predictions at higher orders in perturbation theory show better agreement withmore » the measurements. This work provides the first measurement of the ratio of the differential cross sections of Z + jets and γ + jets production at 13 TeV, as well as the first direct measurement of Z bosons emitted collinearly with a jet.[graphic not available: see fulltext]« less

Measurements of the total and differential fiducial cross sections for the Z boson decaying into two neutrinos are presented at the LHC in proton-proton collisions at a center-of-mass energy of 13 TeV. The data were collected by the CMS detector in 2016 and correspond to an integrated luminosity of 35.9 fb$$^{-1}$$. In these measurements, events are selected containing an imbalance in transverse momentum and one or more energetic jets. The fiducial differential cross section is measured as a function of the Z boson transverse momentum. The results are combined with a previous measurement of charged-lepton decays of the Z boson.more » The measured total fiducial cross section for events with Z boson transverse momentum greater than 200 GeV is $$ {3000}_{-170}^{+180} $$ fb.[graphic not available: see fulltext]« less

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-goingmore » over the Pb-going beam directions are built. In both mass ranges, the differential cross sections as functions of the dimuon transverse momentum p$$_{T}$$ and of a geometric variable ϕ$$^{*}$$ are measured, where ϕ$$^{*}$$ highly correlates with p$$_{T}$$ 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.[graphic not available: see fulltext]« less

Modifications to the distribution of charged particles with respect to high transverse momentum (p$$_{T}$$) jets passing through a quark-gluon plasma are explored using the CMS detector. Back-to-back dijets are analyzed in lead-lead and proton-proton collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.02 TeV via correlations of charged particles in bins of relative pseudorapidity and angular distance from the leading and subleading jet axes. In comparing the lead-lead and proton-proton collision results, modifications to the charged-particle relative distance distribution and to the momentum distributions around the jet axis are found to depend on the dijet momentum balance x$$_{j}$$ , which is themore » ratio between the subleading and leading jet p$$_{T}$$. For events with x$$_{j}$$ ≈ 1, these modifications are observed for both the leading and subleading jets. However, while subleading jets show significant modifications for events with a larger dijet momentum imbalance, much smaller modifications are found for the leading jets in these events.[graphic not available: see fulltext]« less

The performance is presented of the reconstruction and identification algorithms for electrons and photons with the CMS experiment at the LHC. The reported results are based on proton-proton collision data collected at a center-of-mass energy of 13 TeV and recorded in 2016–2018, corresponding to an integrated luminosity of 136 fb^-1. Results obtained from lead-lead collision data collected at √(sNN)=5.02 TeV are also presented. Innovative techniques are used to reconstruct the electron and photon signals in the detector and to optimize the energy resolution. Events with electrons and photons in the final state are used to measure the energy resolution andmore » energy scale uncertainty in the recorded events. The measured energy resolution for electrons produced in Z boson decays in proton-proton collision data ranges from 2 to 5%, depending on electron pseudorapidity and energy loss through bremsstrahlung in the detector material. The energy scale in the same range of energies is measured with an uncertainty smaller than 0.1 (0.3)% in the barrel (endcap) region in proton-proton collisions and better than 1 (3)% in the barrel (endcap) region in heavy ion collisions. The timing resolution for electrons from Z boson decays with the full 2016–2018 proton-proton collision data set is measured to be 200 ps.« less

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 bmore » 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.[graphic not available: see fulltext]« less