• Open Access

Measurement of an Excess in the Yield of J/ψ at Very Low pT in Pb–Pb Collisions at sNN=2.76TeV

J. Adam et al. (ALICE Collaboration)
Phys. Rev. Lett. 116, 222301 – Published 2 June 2016

Abstract

We report on the first measurement of an excess in the yield of J/ψ at very low transverse momentum (pT<0.3GeV/c) in peripheral hadronic Pb-Pb collisions at sNN=2.76TeV, 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 00.3GeV/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.

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  • Received 12 October 2015

DOI:https://doi.org/10.1103/PhysRevLett.116.222301

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

© 2016 CERN, for the ALICE Collaboration

Physics Subject Headings (PhySH)

Nuclear Physics

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Vol. 116, Iss. 22 — 3 June 2016

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