Vector meson photoproduction in UPCs with FoCal

TL;DR

This paper explores the potential of the FoCal detector at ALICE to measure vector meson photoproduction in ultra-peripheral collisions, enabling unprecedented insights into small Bjorken-x physics and gluon saturation phenomena.

Contribution

It presents the physics prospects and capabilities of the new high-granularity FoCal detector for photon-induced measurements at ALICE, focusing on small-x physics exploration.

Findings

FoCal will measure photoproduction cross sections down to x ≈ 7×10⁻⁶ in proton collisions.

FoCal will enable model-independent reconstruction of vector meson production.

The detector will operate from Run 4, enhancing ALICE's physics reach.

Abstract

We discuss the physics prospects of photon-induced measurements using the high-granularity FoCal detector to be installed at the ALICE experiment, covering the pseudorapidity interval $3.4 \leq \eta \leq 5.8$. This new detector, scheduled to be in operation from Run 4, will explore the small Bjorken-$x$ physics region in an unprecedented way. In this region the gluon saturation phenomenon is expected to be dominant. Combined with the rest of the ALICE subdetectors, including the zero degree calorimenters, FoCal will serve to reconstruct in a model-independent way the measured photoproduction cross sections for vectors mesons in a wide range of photon-target energies, down to $x$ values of about $7\times 10^{-6}$ and $2\times 10^{-6}$ in ultra-peripheral photon--proton and photon--lead collisions, respectively.