2,253 research outputs found

    Measurement of the prompt J/psi and psi(2S) polarizations in pp collisions at sqrt(s) = 7 TeV

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    The polarizations of prompt J/psi and psi(2S) mesons are measured in proton-proton collisions at sqrt(s) = 7 TeV, using a dimuon data sample collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.9 inverse femtobarns. The prompt J/psi and psi(2S) polarization parameters lambda[theta], lambda[phi], and lambda[theta, phi], as well as the frame-invariant quantity lambda(tilde), are measured from the dimuon decay angular distributions in three different polarization frames. The J/psi results are obtained in the transverse momentum range 14 < pt < 70 GeV, in the rapidity intervals abs(y) < 0.6 and 0.6 < abs(y) < 1.2. The corresponding psi(2S) results cover 14 < pt < 50 GeV and include a third rapidity bin, 1.2 < abs(y) < 1.5. No evidence of large transverse or longitudinal polarizations is seen in these kinematic regions, which extend much beyond those previously explored

    Measurement of B-s(0) meson production in pp and PbPb collisions at root S-NN=5.02 TeV

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    The production cross sections of B-s(0) mesons and charge conjugates are measured in proton-proton (pp) and PbPb collisions via the exclusive decay channel B-s(0)-> J/ psi phi ->mu(+) mu(-) K+K- at a center-of-mass energy of 5.02 TeV per nucleon pair and within the rapidity range vertical bar y vertical bar <2.4 using the CMS detector at the LHC. The pp measurement is performed as a function of transverse momentum (P-T) of the B-s(0), mesons in the range of 7 to 50 GeV/c and is compared to the predictions of perturbative QCD calculations. The B s production yield in PbPb collisions is measured in two F t intervals, 7 to 15 and 15 to 50 GeV/c, and compared to the yield in pp collisions in the same kinematic region. The nuclear modification factor (R-AA) is found to be 1.5 +/- 0.6(stat) +/- 0.5(syst) for 7-15 GeV/c, and 0.87 +/- 0.30(stat) +/- 0.1 7(syst) for 15-50 GeV/c, respectively. Within current uncertainties, the B-s(0) results are consistent with models of strangeness enhancement, and suppression by parton energy loss, as observed for the B+ mesons. Published by Elsevier B.V.Peer reviewe

    Charged-particle angular correlations in XeXe collisions at root s(NN)=5.44 TeV

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    Azimuthal correlations of charged particles in xenon-xenon collisions at a center-of-mass energy per nucleon pair of root s(NN) = 5.44 TeV are studied. The data were collected by the CMS experiment at the LHC with a total integrated luminosity of 3.42 mu b(-1). The collective motion of the system formed in the collision is parametrized by a Fourier expansion of the azimuthal particle density distribution. The azimuthal anisotropy coefficients v(2), v(3), and v(4) are obtained by the scalar-product, two-particle correlation, and multiparticle correlation methods. Within a hydrodynamic picture, these methods have different sensitivities to noncollective and fluctuation effects. The dependence of the Fourier coefficients on the size of the colliding system is explored by comparing the xenon-xenon results with equivalent lead-lead data. Model calculations that include initial-state fluctuation effects are also compared to the experimental results. The observed angular correlations provide new constraints on the hydrodynamic description of heavy ion collisions.Peer reviewe

    Search for narrow resonances in dilepton mass spectra in proton-proton collisions at root s=13 TeV and combination with 8 TeV data

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    Search for pair production of second-generation leptoquarks at root s=13 TeV

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    A search for pair production of second-generation leptoquarks is performed using proton-proton collision data collected at √s=13  TeV in 2016 with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 35.9  fb−1. Final states with two muons and two jets, or with one muon, two jets, and missing transverse momentum are considered. Second-generation scalar leptoquarks with masses less than 1530(1285) GeV are excluded for β=1.0(0.5), where β is the branching fraction for the decay of a leptoquark to a charged lepton and a quark. The results of the search are also interpreted as limits on the pair production of long-lived top squarks in an R-parity violating supersymmetry model that has a final state with two muons and two jets. These limits represent the most stringent limits to date on these models.Peer reviewe

    Measurements of the pp -> WZ inclusive and differential production cross sections and constraints on charged anomalous triple gauge couplings at root s=13 TeV

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    The WZ production cross section is measured in proton-proton collisions at a centre-of-mass energy = 13 TeV using data collected with the CMS detector, corresponding to an integrated luminosity of 35.9 fb(-1). The inclusive cross section is measured to be sigma(tot)(ppWZ)=48.0) pb, resulting in a total uncertainty of -2.78/+2.98 pb. Fiducial cross section and ratios of charge-dependent cross section measurements are provided. Differential cross section measurements are also presented with respect to three variables: the Z boson transverse momentum p(T), the leading jet p(T), and the M(WZ) variable, defined as the invariant mass of the system composed of the three leptons and the missing transverse momentum. Differential measurements with respect to the W boson p(T), separated by charge, are also shown. Results are consistent with standard model predictions, favouring next-to-next-to-leading-order predictions over those at next-to-leading order. Constraints on anomalous triple gauge couplings are derived via a binned maximum likelihood fit to the M(WZ) variable.Peer reviewe

    Search for the associated production of the Higgs boson and a vector boson in proton-proton collisions at=13 TeV via Higgs boson decays to leptons

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    A search for the standard model Higgs boson produced in association with a W or a Z boson and decaying to a pair of leptons is performed. A data sample of proton-proton collisions collected at p s = 13TeV by the CMS experiment at the CERN LHC is used, corresponding to an integrated luminosity of 35.9 fb. The signal strength is measured relative to the expectation for the standard model Higgs boson, yielding = 2: 5 +1:4. These results are combined with earlier CMS measurements targeting Higgs boson decays to a pair of leptons, performed with the same data set in the gluon fusion and vector boson fusion production modes. The combined signal strength is = 1: 24 +0:29 (1: 00 +0:24 expected), and the observed signi fi cance is 5.5 standard deviations (4.8 expected) for a Higgs boson mass of 125GeV.Peer reviewe

    Search for resonant production of second-generation sleptons with same-sign dimuon events in proton-proton collisions at root s=13 TeV

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    A search is presented for resonant production of second-generation sleptons ((mu) over tilde (L),(nu) over tilde (mu)) via the R-parityviolating coupling. gimel'(211) to quarks, in events with two samesign muons and at least two jets in the final state. The smuon ( muon sneutrino) is expected to decay into amuon and a neutralino (chargino), which will then decay into a second muon and at least two jets. The analysis is based on the 2016 data set of proton- proton collisions at root s = 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb(-1). No significant deviation is observed with respect to standard model expectations. Upper limits on cross sections, ranging from 0.24 to 730 fb, are derived in the context of two simplified models representing the dominant signal contributions leading to a same- sign muon pair. The cross section limits are translated into coupling limits for a modified constrained minimal supersymmetric model with. gimel'(211) as the only nonzero R-parity violating coupling. The results significantly extend restrictions of the parameter space compared with previous searches for similar models.Peer reviewe

    Search for nonresonant Higgs boson pair production in the bbˉ\bar{b}bbˉ\bar{b} final state at √s = 13 TeV

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    Search for pair-produced three-jet resonances in proton-proton collisions at root s=13 TeV

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    A search has been performed for pair-produced resonances decaying into three jets. The proton-proton collision data used for this analysis were collected with the CMS detector in 2016 at a center-of-mass energy of 13 TeV and correspond to an integrated luminosity of 35.9 fb(-1). The mass range from 200 to 2000 GeV is explored in four separate mass regions. The observations show agreement with standard model expectations. The results are interpreted within the framework of R-parity violating SUSY, where pair-produced gluinos decay to a six quark final state. Gluino masses below 1500 GeV are excluded at 95% confidence level. An analysis based on data with multijet events reconstructed at the trigger level extends the reach to masses as low as 200 GeV. Improved analysis techniques have led to enhanced sensitivity, allowing the most stringent limits to date to be set on gluino pair production.Peer reviewe
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