A vendor-unlocked ITS GPU reconstruction in ALICE

Abstract

In LHC Run 3, ALICE experiment’s upgrades enable recording Pb-Pb collisions at a 50 kHz rate using trigger-less continuous readout, managing a peak data rate of 1 TB/s primarily through GPU utilization. Two main phases of data processing exist: the synchronous phase, focused on TPC reconstruction consuming most computing resources, and the asynchronous phase with more GPU resources available. The Inner Tracking System (ITS) has been successfully ported to GPUs for primary vertex finding and track reconstruction, leveraging automatic code generation to support multiple GPU brands with a single code base. This work not only enhances ALICE’s computational capability but also sets a precedent for offloading reconstruction tasks to GPUs in other detectors.