# Quark Matter 2014 - XXIV International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

19-24 May 2014
Europe/Zurich timezone

## Coherent $\psi$(2S) photo-production in ultra-peripheral Pb-Pb collisions at the LHC

20 May 2014, 16:30
2h

### spectrum

Board: G-07
Poster Electromagnetic Probes

### Speaker

Michal Broz (Czech Technical University (CZ))

### Description

Vector mesons are copiously produced in ultra-peripheral nucleus-nucleus collisions In these collisions, the nuclei are separated by an impact parameter larger than the sum of the nuclear radii. The interaction proceeds through the emission of a photon, generated by the electromagnetic field of one of the two nuclei, fluctuating into a quark-antiquark pair,that interacts with the target nucleus. The cross section for this process is sensitive to the gluon distribution in the nucleus and can therefore probe the nuclear gluon shadowing. The ALICE Collaboration has performed the first measurement of the coherent $\psi$(2S) photoproduction cross section in Pb-Pb collisions at the LHC. This charmonium excited state is tagged via the $\psi(2S) \rightarrow l^{+} l^{-}$ and $\psi(2S) \rightarrow J/\psi\pi^{+}\pi^{-}$ decays, where the $J/\psi$ decays into two leptons. The measured cross section and its ratio to the $J/\psi$ cross section are compared to predictions from theoretical models.
On behalf of collaboration: ALICE

### Primary author

Michal Broz (Czech Technical University (CZ))

 Poster