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

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 dσ coh /d y = 0.83 ± 0.19�����stat + syst����� mb. The ψ (2S) ψ (2S) to J/ψ coherent cross section ratio is 0.34+0.08 (stat + syst). The obtained results are compared to theoretical models.