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/ψdecays into two leptons. The analysis is based on an event sample corresponding to an integrated luminosity of about 22μb−1. The cross section for coherent ψ(2S)production in the rapidity interval −0.9 <y <0.9is dσcohψ(2S)/dy =0.83 ±0.19 stat+syst mb. The ψ(2S)to J/ψcoherent cross section ratio is 0.34+0.08−0.07(stat+syst). The obtained results are compared to predictions from theoretical models.