Speaker
Description
The ATLAS Liquid Argon (LAr) calorimeter system provides electromagnetic calorimetry over the pseudo-rapidity range |η| < 3.2 and hadronic and forward calorimetry up to |η| = 4.9. Together with the Tile Calorimeter, it plays a central role in the reconstruction and triggering of electrons, photons, jets, and missing transverse momentum. During LHC Run 3 (2022–2026), the detector operated under increased instantaneous luminosity and pileup conditions, reaching up to about 65 proton-proton interactions per bunch crossing.
Throughout Run 3, the LAr calorimeter was operated within a comprehensive framework combining detector hardware, calibration systems, high-voltage and cryogenic infrastructure, online monitoring, and dedicated software tools. This operational model ensured excellent reliability and data quality, with data-taking efficiencies above 99% and stable detector response throughout the run.
A major evolution during Run 3 was the commissioning and sustained operation of the new fully digital trigger readout path installed during Long Shutdown 2. The system digitizes calorimeter trigger signals at the 40 MHz bunch-crossing rate using on-detector electronics and transmits the data to FPGA-based processing boards installed underground. Approximately 34,000 trigger channels (supercells) are processed in real time, corresponding to input data rates of several tens of terabits per second. The increased trigger-level granularity, up to a factor of ten compared to the legacy system, enables improved identification of electromagnetic objects and better pileup suppression while maintaining low transverse-momentum thresholds. The stable operation of this system allowed the progressive retirement of the legacy analog trigger readout.
This contribution reviews the operational experience and performance of the ATLAS LAr calorimeter during Run 3 and discusses lessons learned for future operation in Run 4 and the High-Luminosity LHC era.