ALICE Time-Of-Flight upgrade

ALICE Time-Of-Flight upgrade
Name	ALICE Time-Of-Flight upgrade
Country	Switzerland
Institution	CERN
Project	ALICE experiment
Detector	Time-of-flight
Status	Upgraded

ALICE Time-Of-Flight upgrade

The ALICE Time-Of-Flight upgrade is a major instrumentation enhancement of the ALICE experiment at CERN carried out to improve particle identification capabilities for heavy-ion collisions recorded in Large Hadron Collider runs. The upgrade replaces and augments existing systems to handle increased luminosity from the LHC and to enable refined measurements relevant to studies initiated by collaborations such as ATLAS, CMS, LHCb, and TOTEM. The program connects to broader efforts in high-energy physics involving institutions like INFN, CERN technical groups, and international consortia from Brookhaven National Laboratory, Lawrence Berkeley National Laboratory, and GSI Helmholtz Centre for Heavy Ion Research.

Background and purpose

The upgrade responds to challenges identified during Run 1 and Run 2 analyses involving the Quark–Gluon Plasma discovered in collisions studied by the ALICE Collaboration and theoretical frameworks from groups like JINR and IHEP. The original Time-of-flight detector architecture, based on Multigap Resistive Plate Chamber technology, faced limitations with the increased interaction rates planned for Run 3 and Run 4 of the Large Hadron Collider. Motivations included achieving better separation of charged hadrons such as pions, kaons, and protons across transverse momentum ranges highlighted by results from PHENIX, STAR, and modeling from Hydro model authors associated with Riken and Lawrence Livermore National Laboratory. The initiative aligns with instrumentation trends seen in experiments like ALICE Inner Tracking System upgrade and detector programs at Fermilab.

Technical design and components

The upgraded system employs advanced Multigap Resistive Plate Chamber modules with optimized gap sizes, new resistive coatings, and refined electrode geometries developed in laboratories including Czech Technical University in Prague, CIEMAT, and University of Birmingham. Front-end electronics integrate custom ASICs produced in collaboration with European Organization for Nuclear Research engineering teams and semiconductor vendors, while high-speed serializers and FPGA logic leverage designs familiar from Xilinx and Intel ecosystems used in Compact Muon Solenoid upgrades. The timing chain includes low-jitter clock distribution derived from systems used by ALICE Time Projection Chamber upgrade and synchronization techniques comparable to those in LHCb upgrade. Mechanical integration uses lightweight carbon-fiber supports and cooling similar to solutions from ATLAS Insertable B-Layer and CMS Phase-1 Upgrade projects. Quality assurance and module production involved partners such as Stony Brook University, University of Turin, Nikhef, and Weizmann Institute of Science.

Detector performance and calibration

The design goal targets single-hit time resolution improvements to the tens-of-picoseconds regime, enabling particle identification benchmarks comparable to advances reported by Belle II and NA61/SHINE. Calibration employs laser-based systems inspired by CMS timing layer methods, time-walk correction algorithms developed alongside groups at University of Geneva and University of Heidelberg, and environmental monitoring informed by sensor work at Max Planck Institute for Physics. Cross-calibration uses reference signals from beam test campaigns at facilities like CERN PS East Area and DESY test beams, with performance validated against Monte Carlo frameworks maintained by GEANT4 and analysis packages from ROOT. Alignment procedures take cues from techniques used in ALICE Inner Tracking System upgrade and ATLAS muon spectrometer operations.

Installation and integration with ALICE

Integration required coordination with ALICE central barrel infrastructure, the ALICE solenoid magnet, and the ALICE Time Projection Chamber services. Installation followed schedules set by CERN accelerator complex maintenance windows, collaborating with groups from European Organization for Nuclear Research cryogenics, vacuum, and safety teams. Cabling and service routing were planned with input from CERN BE Department and executed alongside upgrades to the ALICE detector control system mirroring procedures from LHC Long Shutdown 2. Logistics involved institutions such as University of Frankfurt, University of Warsaw, and Sezione INFN di Bologna for site acceptance testing and final commissioning.

Data acquisition and readout upgrades

To cope with anticipated event rates, the readout chain was overhauled with high-bandwidth links using optical modules compatible with GigaBit Transceiver standards and firmware architectures analogous to those in the ALICE O^2 project. Data flow management integrates back-end servers running software stacks that interface with CERN openlab resources, while real-time processing leverages heterogeneous computing nodes studied by European Grid Infrastructure and CERN IT. Triggerless readout strategies adopt paradigms tested by LHCb upgrade and ATLAS Trigger and Data Acquisition teams to support continuous readout and online calibration.

Commissioning and early results

Commissioning encompassed cosmic-ray runs, calibration with laser systems, and first beam tests during LHC pilot beams observed by coordination with LHC Machine Committee and Beams Department. Early performance metrics reported improved time resolution and increased efficiency consistent with simulations from GEANT4 and analysis using AliRoot frameworks maintained by the ALICE Offline Project. Preliminary physics outputs demonstrated enhanced particle identification enabling refined spectra for light hadrons in collision systems studied alongside analyses from PHENIX and STAR.

Impact on physics program and future developments

The upgrade expands ALICE capabilities for precision measurements of flow coefficients, femtoscopy, and rare probes of the Quark–Gluon Plasma connected to theoretical work from groups such as Institute for Nuclear Theory and Brookhaven National Laboratory. It complements ongoing detector developments like the ALICE Inner Tracking System upgrade and informs future projects at Future Circular Collider studies and experiments at FAIR. Continued R&D on timing layers and ASIC improvements involves collaborations with CERN Microelectronics Group, INFN, and university partners to push toward sub-10-picosecond systems and potential applications in medical imaging and space instrumentation developed by European Space Agency and NASA.

Category:Particle physics detectors Category:ALICE experiment Category:CERN upgrades