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

Adam, J. and Antičić, Tome and Erhardt, Filip and Gotovac, Sven and Mudnić, Eugen and Planinić, Mirko and Poljak, Nikola and Simatović, Goran and Utrobičić, Antonija and Vicković, Linda and Zyzak, M. (ALICE Collaboration) (2016) Measurement of an Excess in the Yield of J/ψ at Very Low pT in Pb–Pb Collisions at √sNN = 2.76  TeV. Physical Review Letters, 116 (22). pp. 222301-13. ISSN 0031-9007

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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.

Item Type: Article
Date: 2 June 2016
Subjects: NATURAL SCIENCES > Physics
Additional Information: © 2016 CERN, for the ALICE Collaboration. Published by the American Physical Society. 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. Received 12 October 2015; published 2 June 2016.
Divisions: Faculty of Science > Department of Physics
Publisher: American Physical Society
Depositing User: Gordana Stubičan Ladešić
Date Deposited: 13 Jul 2016 10:40
Last Modified: 29 Nov 2017 16:48

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