ALICE Upgrade

ALICE Upgrade
Name	ALICE Upgrade
Institution	CERN
Project	Large Hadron Collider
Start	2013
Completed	2022
Field	Particle physics
Detector	ALICE (A Large Ion Collider Experiment)

ALICE Upgrade

The ALICE Upgrade was a major modernization of the ALICE (A Large Ion Collider Experiment) detector at CERN conducted in the 2010s–2020s to enhance studies of quark–gluon plasma, quantum chromodynamics, and heavy-ion collisions at the Large Hadron Collider. It focused on improved tracking, readout, and triggering systems to increase event rates, precision, and sensitivity for rare probes such as heavy-flavor hadrons, quarkonia, and jets. The upgrade involved collaboration among institutions like European Organization for Nuclear Research, national laboratories, and universities across Europe, Asia, and the Americas.

Introduction

The upgrade project built on ALICE's original design conceived for heavy-ion studies during early Large Hadron Collider runs and responded to operational evolutions driven by upgraded LHC luminosity plans, including High Luminosity LHC preparations and schedule coordination with experiments such as ATLAS, CMS, and LHCb. Major stakeholders included CERN, national agencies such as INFN, CNRS, STFC, and research centers like GSI Helmholtz Centre for Heavy Ion Research and Brookhaven National Laboratory. The program aligned with strategies articulated by committees including the CERN Scientific Policy Committee and reviews by panels drawn from the European Strategy for Particle Physics.

Motivation and Scientific Goals

Scientific drivers followed discoveries and open questions from heavy-ion campaigns at the Relativistic Heavy Ion Collider and early LHC runs. Goals emphasized precision measurements of charm quark and beauty quark production, collective phenomena in small systems observed in experiments like PHENIX and STAR, and rare electromagnetic probes previously targeted by experiments such as ALICE, NA60, and WA98. The upgrade aimed to enable high-statistics studies of heavy-flavor hadronization, thermalization of heavy quarks, quarkonium suppression and regeneration relative to results from SPS experiments, and jet quenching comparisons to findings by ATLAS and CMS. Enhanced vertexing and particle identification were motivated by theoretical frameworks from lattice QCD, perturbative QCD, and transport models developed in groups at CERN Theory Division and universities like University of Cambridge and Princeton University.

Detector Upgrades and Technologies

Key hardware changes included a new high-resolution inner tracker using Monolithic Active Pixel Sensors inspired by developments at institutes such as CSEM and groups at Institut Pluridisciplinaire Hubert Curien. The inner tracking system replaced the previous Inner Tracking System with layers of low-mass silicon pixel detectors providing improved impact-parameter resolution for displaced vertices from D meson and B meson decays. A revamped Time Projection Chamber readout moved from multiwire to continuous GEM-based amplification and ALICE front-end electronics similar to systems used in STAR and COMPASS. Upgrades also included a new Fast Interaction Trigger and a revamped Data Acquisition system, leveraging technologies from projects at European Organization for Nuclear Research and computing models akin to Worldwide LHC Computing Grid. Enhancements to Time Of Flight and Electromagnetic Calorimeter readout improved particle identification and electromagnetic probe sensitivity, building on techniques used in PHENIX and CMS electromagnetic calorimetry.

Implementation and Commissioning

Integration and assembly occurred in surface facilities at CERN with contributions from consortia including INFN, CNRS/IN2P3, GSI, TRIUMF, and JINR. Installation campaigns synchronized with the Long Shutdown 2 of the LHC and coordination with maintenance windows for ATLAS, CMS, and LHCb. Commissioning combined cosmic-ray runs, laser calibration systems developed by groups at CERN and test beams at facilities such as CERN Proton Synchrotron and GSI Helmholtz Centre for Heavy Ion Research. Software commissioning leveraged the AliRoot and O2 frameworks and integration tests with Grid computing sites and the LHCb DIRAC model for distributed workflows.

Performance and Early Results

Post-commissioning performance demonstrated improved vertex resolution, tracking efficiency at low transverse momentum, and continuous-readout capability achieving the designed interaction-rate goals. Early physics-quality data allowed refined measurements of charm-hadron spectra, D-meson elliptic flow comparable to analyses published by STAR and PHENIX, and improved studies of low-mass dielectrons complementing results from NA60. First results informed model comparisons with predictions from lattice QCD and transport calculations developed at institutions like GSI and CERN Theory Division, and helped refine global analyses including inputs used by the European Centre for Nuclear Research community.

Collaboration, Funding, and Timeline

The upgrade was executed by the ALICE Collaboration comprising hundreds of institutes from Europe, Asia, and the Americas, with institutional partners including University of Bonn, Czech Technical University in Prague, Seoul National University, University of São Paulo, and Yale University. Funding came from national agencies such as INFN, CNRS, DFG, RCUK, NSF, MEXT, and FAPESP, coordinated with CERN contributions and in-kind deliveries from laboratories like Brookhaven National Laboratory and TRIUMF. The timeline aligned procurement, prototyping, and installation phases to the LHC Long Shutdown schedule, culminating in full detector operation as the LHC Run 3 program commenced.

Category:Particle detectors Category:CERN experiments