Photoproduction in Ultra-Peripheral Relativistic Heavy Ion Collisions at STAR

TL;DR

This paper reports on STAR experiment results observing vector-meson photoproduction, including $ ho^0(770)$ and $ ho^0$ excited states, in ultra-peripheral heavy ion collisions at RHIC, highlighting electromagnetic interactions at high energies.

Contribution

It provides new experimental data on vector-meson photoproduction and excited states in ultra-peripheral heavy ion collisions at RHIC.

Findings

Observation of $ ho^0(770)$ production at various energies.

Detection of $ ho^0$ excited states via $ ho^0 o ho^0$ decay channels.

First measurements of photoproduction of $ ho^0$ excited states in this context.

Abstract

In ultra-peripheral relativistic heavy ion collisions the beam ions scatter at impact parameters larger than the sum of their radii, so that they interact via long range electromagnetic forces. Due to the Lorentz-boost of the beam particles, the exchanged virtual photons have high energies and can induce the photoproduction of vector-mesons. We present recent results of the STAR experiment at RHIC on $\rho^0(770)$ production in Au-Au ultra-peripheral collisions at various energies. STAR has also observed the photoproduction of $\pi^+\pi^-\pi+\pi^-$, which is related to the still poorly known excited states of the $\rho^0$.