ALICE Upgrades

TL;DR

The ALICE experiment is undergoing upgrades including a high-granularity calorimeter and advanced tracking sensors for Run 4, and a comprehensive new detector system, ALICE 3, for Run 5 and beyond, to enhance heavy-ion physics measurements.

Contribution

This paper details the design and planned implementation of new detector systems and upgrades for ALICE to improve measurements of heavy-ion collisions and quark-gluon plasma properties.

Findings

Enhanced neutral pion and photon measurements with FoCal.

Improved tracking resolution with wafer-scale sensors.

New capabilities for probing QGP and chiral symmetry restoration.

Abstract

The ALICE collaboration prepares multiple upgrades to further extend the reach of heavy-ion physics at the LHC. For LHC Run 4 (2030-2033), a Forward Calorimeter (FoCal) system combines a high-granularity electromagnetic silicon-tungsten calorimeter with a conventional hadronic calorimeter leading to an excellent two-shower separation for neutral pion reconstruction and photon isolation. Direct photon measurements with FoCal will uniquely constrain the low-x gluon structure of protons and nuclei via forward measurements of direct photons. Additionally, ALICE will employ bent, wafer-scale pixel sensors achieving truly cylindrical tracking layers with very low material budget. These layers will replace the three innermost layers of the Inner Tracking System resulting in an improvement in pointing resolution allowing new measurements of heavy-flavour hadrons and dielectrons. For Run 5 and beyond, a next-generation detector system, ALICE 3, has been conceived to gain unique access to the interaction and thermalization of heavy flavour probes in the QGP as well as to the thermal radiation carrying information about the temperature and the restoration of chiral symmetry. At its core, it combines a high-resolution vertex detector with a large-acceptance silicon pixel tracker. For the identification of particles, a combination of a time-of-flight system, a ring-imaging Cherenkov detector, an electromagnetic calorimeter, a muon identifier, and a dedicated forward detector for ultra-soft photons, are envisaged.