Measurement of an Excess in the Yield of J/psi at Very Low p(T) in Pb-Pb Collisions at √s(NN)=2.76 TeV

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Abstract

We report on the first measurement of an excess in the yield of J/ψ at very low transverse momentum (pT<0.3  GeV/c) in peripheral hadronic Pb-Pb collisions at sNN−−−√=2.76  TeV, performed by ALICE at the CERN LHC. Remarkably, the measured nuclear modification factor of J/ψ in the rapidity range 2.5<y<4 reaches about 7 (2) in the pT range 0–0.3  GeV/c in the 70%–90% (50%–70%) centrality class. The J/ψ production cross section associated with the observed excess is obtained under the hypothesis that coherent photoproduction of J/ψ is the underlying physics mechanism. If confirmed, the observation of J/ψ coherent photoproduction in Pb-Pb collisions at impact parameters smaller than twice the nuclear radius opens new theoretical and experimental challenges and opportunities. In particular, coherent photoproduction accompanying hadronic collisions may provide insight into the dynamics of photoproduction and nuclear reactions, as well as become a novel probe of the quark-gluon plasma.

Journal

  • Physical review letters

    Physical review letters 116(22), 222301, 2016-06

    American Physical Society

Keywords

Codes

  • NII Article ID (NAID)
    120005818354
  • NII NACSIS-CAT ID (NCID)
    AA00773679
  • Text Lang
    ENG
  • Article Type
    journal article
  • ISSN
    0031-9007
  • Data Source
    IR 
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