Photoproduction of rho0 in ultra--peripheral nuclear collisions at ALICE

TL;DR

This paper reports on the measurement of rho0 meson photoproduction in ultra-peripheral lead-lead collisions at the LHC, demonstrating the highest photon-nucleus energies achieved and utilizing ALICE's capabilities for low transverse momentum detection.

Contribution

It presents the first analysis of rho0 photoproduction at unprecedented energies in ultra-peripheral heavy-ion collisions at the LHC.

Findings

High cross section for rho0 production observed

Photon-nucleus energy exceeds previous experiments

ALICE's low pT tracking enables detailed analysis

Abstract

Photoproduction of $\rho^0$ mesons in ultra-peripheral Pb+Pb collisions has been studied by the ALICE Collaboration at the CERN LHC. The strong photon flux associated with relativistic charged nuclei leads to a very large cross section for exclusive photoproduction of $\rho^0$ meson in interactions of the type $Pb + Pb \rightarrow Pb + Pb + \rho^0$. For a $\rho^0$ produced at mid-rapidity at the LHC, the photon-nucleus center of mass energy is higher than in any previous experiment. The ALICE detector is a general purpose detector dedicated to study heavy--ion collisions. ALICE has excellent performance in the low $p_T$ region, and can reconstruct charged particle tracks with 0.1 GeV/c $\leq p_T \leq 100$ GeV/c. In this analysis all tracks were required to be within ALICE's central barrel. Analysis of data from the first heavy ion run at the LHC in 2010 will be discussed in this paper.