Physics performance of the ALICE Forward Calorimeter upgrade

The ALICE Collaboration proposes to instrument the existing ALICE detector with a forward calorimeter system (FoCal), planned to take data during LHC Run 4 (2029$-$2032). The FoCal detector is a highly-granular Si+W electromagnetic calorimeter combined with a conventional sampling hadronic calorimeter, covering the pseudo-rapidity interval of $3.2<\eta<5.8$. The FoCal design is optimized to measure isolated photons at forward rapidity for $p_{\rm T}\gtrsim4$ GeV/$c$, as well as neutral hadrons, vector mesons, and jets. Measurements of the inclusive distributions and correlations of these observables probe the structure of matter down to $x\sim10^{-6}$, providing incisive tests of linear and non-linear QCD evolution at low $x$. This document presents current projections of the FoCal measurement performance for these observables.