Coherent ψ(2S) photo-production in ultra-peripheral Pb–Pb collisions at √sNN=2.76 TeV

Adam, J. and Adamová, D. and Aggarwal, M. M. and Aglieri, Rinella G. and Agnello, M. and Barnaföldi, Gergely Gábor and Bencédi, Gyula and Berényi, Dániel and Boldizsár, László and Dénes, Ervin and Hamar, Gergő and Kiss, Gábor and Varga-Kőfaragó, Mónika and Lévai, Péter and Oláh, László and Pochybova, Sona (2015) Coherent ψ(2S) photo-production in ultra-peripheral Pb–Pb collisions at √sNN=2.76 TeV. PHYSICS LETTERS B, 751. pp. 358-370. ISSN 0370-2693

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Abstract

We have performed the first measurement of the coherent ψ(2S) photo-production cross section in ultra-peripheral Pb–Pb collisions at the LHC. This charmonium excited state is reconstructed via the ψ(2S) → l+l− and ψ(2S) → J/ ψπ+ π− decays, where the J/ ψ decays into two leptons. The analysis is based on an event sample corresponding to an integrated luminosity of about 22 μb−1. The cross section for coherent ψ(2S) production in the rapidity interval −0.9 < y < 0.9 is d σ coh ψ(2S)/dy = 0.83 ± 0.19(stat + syst) mb. The ψ(2S) to J/ ψ coherent cross section ratio is 0.34+0.08 −0.07(stat + syst). The obtained results are compared to predictions from theoretical models.

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