• Open Access

Exclusive J/ψ Photoproduction off Protons in Ultraperipheral p-Pb Collisions at sNN=5.02TeV

B. Abelev et al. (ALICE Collaboration)
Phys. Rev. Lett. 113, 232504 – Published 5 December 2014

Abstract

We present the first measurement at the LHC of exclusive J/ψ photoproduction off protons, in ultraperipheral proton-lead collisions at sNN=5.02TeV. Events are selected with a dimuon pair produced either in the rapidity interval, in the laboratory frame, 2.5<y<4 (pPb) or 3.6<y<2.6 (Pbp), and no other particles observed in the ALICE acceptance. The measured cross sections σ(γ+pJ/ψ+p) are 33.2±2.2(stat)±3.2(syst)±0.7(theor)nb in pPb and 284±36(stat)32+27(syst)±26(theor)nb in Pbp collisions. We measure this process up to about 700 GeV in the γp center of mass, which is a factor of two larger than the highest energy studied at HERA. The data are consistent with a power law dependence of the J/ψ photoproduction cross section in γp energies from about 20 to 700 GeV, or equivalently, from Bjorken x scaling variable between 2×102 and 2×105, thus indicating no significant change in the gluon density behavior of the proton between HERA and LHC energies.

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  • Received 1 July 2014

DOI:https://doi.org/10.1103/PhysRevLett.113.232504

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.

© 2014 CERN, for the The ALICE Collaboration

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Vol. 113, Iss. 23 — 5 December 2014

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