128 Search Results

For the first time at LHC energies, the forward rapidity gap spectra from proton-lead collisions for both proton and lead dissociation processes are presented. The analysis is performed over 10.4 units of pseudorapidity at a center-of-mass energy per nucleon pair of $$\sqrt{s_{NN}}$$ = 8.16 TeV , almost 300 times higher than in previous measurements of diffractive production in proton-nucleus collisions. For lead dissociation processes, which correspond to the pomeron-lead event topology, the EPOS-LHC generator predictions are a factor of 2 below the data, but the model gives a reasonable description of the rapidity gap spectrum shape. For the pomeron-proton topology,more » the EPOS-LHC, QGSJET II, and HIJING predictions are all at least a factor of 5 lower than the data. The latter effect might be explained by a significant contribution of ultraperipheral photoproduction events mimicking the signature of diffractive processes. These data may be of significant help in understanding the high energy limit of quantum chromodynamics and for modeling cosmic ray air showers.« 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

The second-order Fourier coefficients ( $v_2$) characterizing the azimuthal distributions of Υ(1S) and Υ(2S) mesons produced in PbPb collisions at $\sqrt{s_{{}_{\mathrm{NN}}}}=5.02\text{TeV}$ are studied. The Υ mesons are reconstructed in their dimuon decay channel, as measured by the CMS detector. The collected data set corresponds to an integrated luminosity of $1.7{\text{nb}}^{-1}$. The scalar product method is used to extract the ${more »}_{}$ v 2 coefficients of the azimuthal distributions. Results are reported for the rapidity range $\left|y\right|<2.4$, in the transverse momentum interval $0<p_{\mathrm{T}}<50\text{GeV}/c$, and in three centrality ranges of 10–30%, 30–50% and 50–90%. In contrast to the $\mathrm{J}/\mathit{\psi }$ mesons, the measured $v_2$ values for the Image 5 mesons are found to be consistent with zero.« less

Results of the Model Unspecific Search in CMS (MUSiC), using proton–proton collision data recorded at the LHC at a centre-of-mass energy of 13TeV, corresponding to an integrated luminosity of 35.9 fb^-1, are presented. The MUSiC analysis searches for anomalies that could be signatures of physics beyond the standard model. The analysis is based on the comparison of observed data with the standard model prediction, as determined from simulation, in several hundred final states and multiple kinematic distributions. Events containing at least one electron or muon are classified based on their final state topology, and an automated search algorithm surveys themore » observed data for deviations from the prediction. The sensitivity of the search is validated using multiple methods. No significant deviations from the predictions have been observed. For a wide range of final state topologies, agreement is found between the data and the standard model simulation. This analysis complements dedicated search analyses by significantly expanding the range of final states covered using a model independent approach with the largest data set to date to probe phase space regions beyond the reach of previous general searches.« 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

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

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

This paper presents new sets of parameters (“tunes”) for the underlying-event model of the $${\textsc {herwig}} \,7$$ event generator. These parameters control the description of multiple-parton interactions (MPI) and colour reconnection in $${\textsc {herwig}} \,7$$, and are obtained from a fit to minimum-bias data collected by the CMS experiment at $$\sqrt{s}=0.9$$, 7, and $$13 \,\text {Te}\text {V} $$. The tunes are based on the NNPDF 3.1 next-to-next-to-leading-order parton distribution function (PDF) set for the parton shower, and either a leading-order or next-to-next-to-leading-order PDF set for the simulation of MPI and the beam remnants. Predictions utilizing the tunes are produced for eventmore » shape observables in electron-positron collisions, and for minimum-bias, inclusive jet, top quark pair, and Z and W boson events in proton-proton collisions, and are compared with data. Each of the new tunes describes the data at a reasonable level, and the tunes using a leading-order PDF for the simulation of MPI provide the best description of the data.« less

The CP -violating weak phase ${\varphi }_{\mathrm{s}}$ and the decay width difference $\mathrm{\Delta }{\mathrm{\Gamma }}_{\mathrm{s}}$ between the light and heavy ${\mathrm{B}}_s^0$ mass eigenstates are measured with the CMS detector at the LHC in a sample of $48500$ reconstructed ${\mathrm{B}}_s^0\to \mathrm{J}/\mathrm{\psi }\mathrm{\varphi }\left(1020\right)\to {\mathrm{\mu }}^{+more »}$ μ − K + K − events. The measurement is based on a data sample corresponding to an integrated luminosity of $96.4{\text{fb}}^{-1}$ , collected in proton-proton collisions at $\sqrt{s}=13\text{TeV}$ in 2017–2018. To extract the values of ${\varphi }_{\mathrm{s}}$ and $\mathrm{\Delta }{\mathrm{\Gamma }}_{\mathrm{s}}$ , a time-dependent and flavor-tagged angular analysis of the ${\mathrm{\mu }}^{+}{\mathrm{\mu }}^{-}{\mathrm{K}}^{+}{\mathrm{K}}^{-}$ final state is performed. The analysis employs a dedicated tagging trigger and a novel opposite-side muon flavor tagger based on machine learning techniques. The measurement yields ${\varphi }_{\mathrm{s}}=-11\pm 50\text{(stat)}\pm 10\text{(syst)}\text{mrad}$ and $\mathrm{\Delta }{\mathrm{\Gamma }}_{\mathrm{s}}=0.114\pm 0.014\text{(stat)}\pm 0.007\text{(syst)}{\text{ps}}^{-1}$ , in agreement with the standard model predictions. When combined with the previous CMS measurement at $\sqrt{s}=8\text{TeV}$ , the following values are obtained: ${\varphi }_{\mathrm{s}}=-21\pm 44\text{(stat)}\pm 10\text{(syst)}\text{mrad}$ , $\mathrm{\Delta }{\mathrm{\Gamma }}_{\mathrm{s}}=0.1032\pm 0.0095\text{(stat)}\pm 0.0048\text{(syst)}{\text{ps}}^{-1}$ , a significant improvement over the 8 TeV result.« less