Charmonium and e(+)e(-) pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at root s(NN)=2.76 TeV

Abbas, E. and Abelev, B. and Adam, J. and Adamova, D. and Adare, A. M. and Aggarwal, M. M. and Rinella, G. A. and Agnello, M. and Agócs, András and Agostinelli, A. and Ahammed, Z. and Ahmad, N. and Masoodi, A. A. and Ahmed, I. and Ahn, S. A. and Ahn, S. U. and Aimo, I. and Ajaz, M. and Akindinov, A. and Aleksandrov, D. and Alessandro, B. and Alexandre, D. and Alici, A. and Alkin, A. and Avina, E. A. and Alme, J. and Alt, T. and Altini, V. and Altinpinar, S. and Altsybeev, I. and Barnaföldi, Gergely Gábor and Bencédi, Gyula and Berényi, Dániel and Boldizsár, László and Dénes, Ervin and Hamar, Gergő and Lévai, Péter and Molnár, Levente and Pochybova, Sona (2013) Charmonium and e(+)e(-) pair photoproduction at mid-rapidity in ultra-peripheral Pb-Pb collisions at root s(NN)=2.76 TeV. EUROPEAN PHYSICAL JOURNAL C, 73 (11). ISSN 1434-6044

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Abstract

The ALICE Collaboration at the LHC has measured the J / ψ and ψ ′ photoproduction at mid-rapidity in ultra-peripheral Pb-Pb-collisions at √sNN=2.76 TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 23 µ b − 1 . The cross section for coherent and incoherent J / ψ production in the rapidity interval -0.9 < y < 0.9, are d σ coh J/ψ / dy = 2 .38 + 0 .34 − 0 .24 sta +sys mb. and d σ inc J/ψ / dy = 0 .98 + 0 .19 − 0 .17 sta +sys mb, respectively. The results are compared to theoretical models for J / ψ production and the coherent cross section is found to be in good agreement with those models incorporating moderate nuclear gluon shadowing, such as EPS09 parametrization. In addition the cross section for the process γγ → e + e − has been measured and found to be in agreement with models implementing QED at leading order.

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