7 research outputs found

    Coherent J/psi photoproduction in ultra-peripheral PbPb collisions at root s(NN)=2.76 TeV with the CMS experiment

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    Coherent J/psi photoproduction in ultra-peripheral PbPb collisions at root s(NN)=2.76 TeV with the CMS experiment

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    The cross section for coherent J/psi photoproduction accompanied by at least one neutron on one side of the interaction point and no neutron activity on the other side, Xn0n, is measured with the CMS experiment in ultra-peripheral PbPb collisions at root sNN= 2.76TeV. The analysis is based on a data sample corresponding to an integrated luminosity of 159 mu b(-1), collected during the 2011 PbPb run. The J/psi mesons are reconstructed in the dimuon decay channel, while neutrons are detected using zero degree calorimeters. The measured cross section is d sigma(Xn)o(n)(coh)/dy(J/psi) = 0.36 +/- 0.04 (stat)+/- 0.04 (syst) mbin the rapidity interval 1.8 <vertical bar y vertical bar < 2.3. Using a model for the relative rate of coherent photoproduction processes, this Xn0nmeasurement gives a total coherent photoproduction cross section of d sigma(coh/) dy(J/psi) = 1.82 +/- 0.22 (stat)+/- 0.20 (syst)+/- 0.19 (theo) mb. The data strongly disfavorthe impulse approximation model prediction, indicating that nuclear effects are needed to describe coherent J/psi photoproduction in.+ Pbinteractions. The data are found to be consistent with the leading twist approximation, which includes nuclear gluon shadowing. (C) 2017 The Author(s). Published by Elsevier B.V

    Search for new resonances decaying via WZ to leptons in proton-proton collisions <tex>\sqrt{s}=$</tex>8 TeV

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    Strange hadron collectivity in pPb and PbPb collisions

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    Abstract The collective behavior of K S 0 KS0 {\textrm{K}}_{\textrm{S}}^0 and Λ / Λ ÂŻ Λ/Λ‟ \Lambda /\overline{\Lambda} strange hadrons is studied by measuring the elliptic azimuthal anisotropy (v 2) using the scalar-product and multiparticle correlation methods. Proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy s NN sNN \sqrt{s_{\textrm{NN}}} = 8.16 TeV and lead-lead (PbPb) collisions at s NN sNN \sqrt{s_{\textrm{NN}}} = 5.02 TeV collected by the CMS experiment at the LHC are investigated. Nonflow effects in the pPb collisions are studied by using a subevent cumulant analysis and by excluding events where a jet with transverse momentum greater than 20 GeV is present. The strange hadron v 2 values extracted in pPb collisions via the four- and six-particle correlation method are found to be nearly identical, suggesting the collective behavior. Comparisons of the pPb and PbPb results for both strange hadrons and charged particles illustrate how event-by-event flow fluctuations depend on the system size

    Strange hadron collectivity in pPb and PbPb collisions

    No full text
    The collective behavior of KS0 {\textrm{K}}_{\textrm{S}}^0 and Λ/Λ‟ \Lambda /\overline{\Lambda} strange hadrons is studied by measuring the elliptic azimuthal anisotropy (v2_{2}) using the scalar-product and multiparticle correlation methods. Proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy sNN \sqrt{s_{\textrm{NN}}} = 8.16 TeV and lead-lead (PbPb) collisions at sNN \sqrt{s_{\textrm{NN}}} = 5.02 TeV collected by the CMS experiment at the LHC are investigated. Nonflow effects in the pPb collisions are studied by using a subevent cumulant analysis and by excluding events where a jet with transverse momentum greater than 20 GeV is present. The strange hadron v2_{2} values extracted in pPb collisions via the four- and six-particle correlation method are found to be nearly identical, suggesting the collective behavior. Comparisons of the pPb and PbPb results for both strange hadrons and charged particles illustrate how event-by-event flow fluctuations depend on the system size.[graphic not available: see fulltext

    Strange hadron collectivity in pPb and PbPb collisions

    No full text
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