Speaker
Description
During the last ten years the detector agnostic open source track reconstruction toolkit ACTS has matured to production level quality and is used in offline data taking in ATLAS, sPHENIX, FASER, and is part of many upgrade and feasibility studies within the community at large. For ATLAS, the ACTS based track reconstruction has surpassed the legacy setup for the predicted Phase-2 performance in computational efficiency, while retaining the same or partly improving on the physics performance. Underpinned by the ATLAS initiative for a technology choice of the high level trigger farm for HL-LHC, a dedicated R&D effort has taken place to reimplement the same conceptual track reconstruction for massively parallel hardware, particularly targeting GPGPUs. This development followed the design principle to strictly avoid compromises (algorithmically and numerically) in physics performance and has led to the creation of several individual leaf libraries that are tightly connected to the corresponding ACTS equivalents. The detray library allows for a GPU friendly geometry description of generic detectors that can be automatically generated from an ACTS tracking geometry description without loss of precision in describing the geometry and material content of the detector. The covfie library enables a generic description of covariant vector fields and can be used to accurately describe and access the magnetic field needed for track propagation on host and device; it has also been adopted by the AdePT project aiming at a Geant4 based full simulation on GPGPUs. The algorithmic code of clustering, seeding, track finding and fitting, together with the necessary components of track propagation have been implemented in detray and traccc to match the algorithmic performance of the corresponding ACTS algorithms, while achieving a remarkable relative speedup with respect to full CPU based processing. We present the physics and computational performance of both ACTS and traccc using the ColliderML dataset, that has been simulated with Geant4 and the OpenDataDetector. Furthermore, we demonstrate the level of compatibility of results in this heterogeneous setup and augment this with a discussion about numerical stability and prospects of long term maintenance. Where possible, we translate those results onto applications of clients of ACTS, most prominently the ATLAS Phase-2 upgrade ITk.