189 research outputs found

    Observation of Charge-Dependent Azimuthal Correlations in p-Pb Collisions and Its Implication for the Search for the Chiral Magnetic Effect

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    Pseudorapidity distributions of charged hadrons in proton-lead collisions at root s(NN)=5:02 and 8.16 TeV

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    The pseudorapidity distributions of charged hadrons in proton-lead collisions at nucleon-nucleon center-of-mass energies root s(NN) = 5.02 and 8.16 TeV are presented. The measurements are based on data samples collected by the CMS experiment at the LHC. The number of primary charged hadrons produced in non-single-diffractive proton-lead collisions is determined in the pseudorapidity range vertical bar eta(lab)vertical bar vertical bar(vertical bar eta cm vertical bar) <0.5 are 17.1 +/- 0.01 (stat) +/- 0.59 (syst) and 20.10 +/- 0.01 (stat) +/- 0.5(syst) at root s(NN) = 5.02 and 8.16 TeV, respectively. The particle densities per participant nucleon are compared to similar measurements in proton-proton, proton-nucleus, and nucleus-nucleus collisions.Peer reviewe

    Search for Supersymmetry in pp Collisions at root s=13 TeV in the Single-Lepton Final State Using the Sum of Masses of Large-Radius Jets

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    Observation of Two Excited B-c(+) States and Measurement of the B-c(+) (2S) Mass in pp Collisions at root s=13 TeV

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    Signals consistent with the B-c(+)(2S) and B-c*(+)(2S) states are observed in proton-proton collisions at root s = 13 TeV, in an event sample corresponding to an integrated luminosity of 143 fb(-1), collected by the CMS experiment during the 2015-2018 LHC running periods. These excited (b) over barc states are observed in the B-c(+)pi(+)pi(-) invariant mass spectrum, with the ground state B-c(+) reconstructed through its decay to J/psi pi(+). The two states are reconstructed as two well-resolved peaks, separated in mass by 29.1 +/- 1.5(stat) +/- 0.7(syst) MeV. The observation of two peaks, rather than one, is established with a significance exceeding five standard deviations. The mass of the B-c(+)(2S) meson is measured to be 6871.0 +/- 1.2(stat) +/- 0.8(syst) +/- 0.8(B-c(+)) MeV, where the last term corresponds to the uncertainty in the world-average B-c(+) mass.Peer reviewe

    Constraints on anomalous Higgs boson couplings using production and decay information in the four-lepton final state

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    © 2017 The Author A search is performed for anomalous interactions of the recently discovered Higgs boson using matrix element techniques with the information from its decay to four leptons and from associated Higgs boson production with two quark jets in either vector boson fusion or associated production with a vector boson. The data were recorded by the CMS experiment at the LHC at a center-of-mass energy of 13TeV and correspond to an integrated luminosity of 38.6fb −1 . They are combined with the data collected at center-of-mass energies of 7 and 8TeV, corresponding to integrated luminosities of 5.1 and 19.7fb −1 , respectively. All observations are consistent with the expectations for the standard model Higgs boson

    Search for Zγ resonances using leptonic and hadronic final states in proton-proton collisions at √s=13 TeV

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    A search is presented for resonances decaying to a Z boson and a photon. The analysis is based on data from proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb−1, and collected with the CMS detector at the LHC in 2016. Two decay modes of the Z boson are investigated. In the leptonic channels, the Z boson candidates are reconstructed using electron or muon pairs. In the hadronic channels, they are identified using a large-radius jet, containing either light-quark or b quark decay products of the Z boson, via jet substructure and advanced b quark tagging techniques. The results from these channels are combined and interpreted in terms of upper limits on the product of the production cross section and the branching fraction to Zγ for narrow and broad spin-0 resonances with masses between 0.35 and 4.0 TeV, providing thereby the most stringent limits on such resonances.[Figure not available: see fulltext.]

    Measurement of b hadron lifetimes in pp collisions at root s=8TeV

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    Correction: DOI:10.1140/epjc/s10052-018-6014-7Measurements are presented of the lifetimes of the B-0, B-s(0), Lambda(0)(b), and B-c(+) hadrons using the decay channels B-0 -> J/psi K*(892)(0), B-0 -> J/psi K-S(0), B-s(0) -> J/psi pi(+)pi(-), B-s(0) -> J/psi phi(1020), Lambda(0)(b) -> J/psi Lambda(0), and B-c(+) -> J/psi pi(+). The data sample, corresponding to an integrated luminosity of 19.7 fb(-1), was collected by the CMS detector at the LHC in proton-proton collisions at root s = 8TeV. The B-0 life-time is measured to be 453.0 +/- 1.6 (stat) +/- 1.8 (syst) mu m in J/psi K*(892)(0) and 457.8 +/- 2.7 (stat) +/- 2.8 (syst) mu m in J/psi K-S(0), which results in a combined measurement of c tau(0) = 454.1 +/- 1.4 (stat) +/- 1.7 (syst) mu m. The effective lifetime of the B-s(0) meson is measured in two decay modes, with contributions from different amounts of the heavy and light eigenstates. This results in two different measured lifetimes: c tau(0)(Bs) -> J/psi pi(+)pi(-) = 502.7 +/- 10.2 (stat) +/- 3.4 (syst) mu m and c tau(0)(Bs) -> J/psi phi(1020) = 443.9 +/- 2.0 (stat) +/- 1.5 (syst) mu m. The Lambda(0)(b) lifetime is found to be 442.9 +/- 8.2 (stat) +/- 2.8 (syst) mu m. The precision from each of these channels is as good as or better than previous measurements. The B-c(+) lifetime, measured with respect to the B+ to reduce the systematic uncertainty, is 162.3 +/- 7.8 (stat) +/- 4.2 (syst) +/- 0.1 (tau(B+)) mu m. All results are in agreement with current world-average values.Peer reviewe

    Search for natural and split supersymmetry in proton-proton collisions at root s=13 TeV in final states with jets and missing transverse momentum

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    A search for supersymmetry (SUSY) is performed in final states comprising one or more jets and missing transverse momentum using data from proton-proton collisions at a centre-of-mass energy of 13 TeV. The data were recorded with the CMS detector at the CERN LHC in 2016 and correspond to an integrated luminosity of 35.9 fb(-1). The number of signal events is found to agree with the expected background yields from standard model processes. The results are interpreted in the context of simplified models of SUSY that assume the production of gluino or squark pairs and their prompt decay to quarks and the lightest neutralino. The masses of bottom, top, and mass-degenerate light-flavour squarks are probed up to 1050, 1000, and 1325 GeV, respectively. The gluino mass is probed up to 1900, 1650, and 1650 GeV when the gluino decays via virtual states of the aforementioned squarks. The strongest mass bounds on the neutralinos from gluino and squark decays are 1150 and 575 GeV, respectively. The search also provides sensitivity to simplified models inspired by split SUSY that involve the production and decay of long-lived gluinos. Values of the proper decay length CT0 from 10(-3) to 10(5) mm are considered, as well as a metastable gluino scenario. Gluino masses up to 1750 and 900 GeV are probed for CT0 = 1mm and for the metastable state, respectively. The sensitivity is moderately dependent on model assumptions for CT0 greater than or similar to 1 m. The search provides coverage of the CT0 parameter space for models involving long-lived gluinos that is complementary to existing techniques at the LHC.Peer reviewe

    Measurement of the B-+/- Meson Nuclear Modification Factor in Pb-Pb Collisions at root s(NN)=5.02 TeV

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    Measurements of t(t)over-bar cross sections in association with b jets and inclusive jets and their ratio using dilepton final states in pp collisions at root s=13 TeV

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    The cross sections for the production of t (t) over bar b (b) over bar and t (t) over bar jj events and their ratio sigma(t (t) over bar b (b) over bar)/sigma(t (t) over bar jj) are measured using data corresponding to an integrated luminosity of 2.3 fb(-1) collected in pp collisions at root s = 13 TeV with the CMS detector at the LHC. Events with two leptons (e or mu) and at least four reconstructed jets, including at least two identified as b quark jets, in the final state are selected. In the full phase space, the measured ratio is 0.022 +/- 0.003 (stat) +/- 0.006 (syst), the cross section sigma(t (t) over bar b (b) over bar) bis 4.0 +/- 0.6 (stat)+/- 1.3 (syst) pb and sigma(t (t) over bar jj) is 184 +/- 6 (stat)+/- 33 (syst) pb. The measurements are compared with the standard model expectations obtained from a POWHEG simulation at next-to-leading-order interfaced with PYTHIA. (c) 2017 The Author. Published by Elsevier B.V.Peer reviewe
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