Analysis of Test Beam Data for the ATLAS High-Granularity Timing Detector and Jet Flavor-Tagging Studies: Exploring Pile-Up Interactions from Detector- and Reconstruction Perspectives

Sammanfattning

The increase in the number of simultaneous proton-proton collisions, pile-up interactions, will be a major challenge for the future High-Luminosity phase of the Large Hadron Collider (LHC) at CERN, making pile-up mitigation an important issue for the ATLAS experiment. The High-Granularity Timing Detector (HGTD), to be installed in the upcoming years, is one of the detector upgrades contributing to this pile-up mitigation. To report the current status of the HGTD development, an HGTD test-beam analysis was performed using data taken during two weeks in October 2025 at the CERN SPS test-beam facility. Synchronization between different detector systems in the test-beam environment was achieved. The full data reconstruction chain was demonstrated to be feasible although the measured hit efficiency and timing resolution were limited by non-optimal chip tuning including a very high threshold setting, as well as by low statistics. To study the effect of pile-up, the impact of jet pile-up contamination on the jet flavor-tagger was investigated under current LHC running conditions. A substantial degradation in flavor-tagging performance was seen, highlighting the importance of understanding pile-up effects in jet reconstruction. A supplementary timing-based pile-up mitigation study was also performed.