Speaker
Description
At the future colliders such as High-Luminosity LHC (HL-LHC), the average number of the simultaneous pp interactions per event, or pile-up (µ), will rise from current 30-60 to as much as 200. Among the full event simulation and reconstruction chains, reconstruction of charged particles quickly becomes the most computationally intensive chain because it scales combinatorially with an increasing number of charged particles. Resolving the ambiguity using time measurement has already been investigated during LHC Phase-II Upgrade, e.g. the ATLAS High Granularity Timing Detector (HGTD), which will be placed outside the ATLAS Phase-II Inner Tracker (ITk) endcap to remove the pile-up vertex in the forward region of 2.4< |eta| < 4. Meanwhile, the possibility of replacing the inner layers of the ATLAS Phase-II barrel pixel detector with 4D pixel detector during a possible Phase-III upgrade is foreseen as well.
Based on the common tracking software, ACTS, where the particle flight time is integrated in the track parameterization inherently, the gain of tracking performance by including time measurement in low-level cluster, seeding and track following has been explored on top of dedicated 4D digitization. In this contribution, we will present the implementation of the ACTS-based 4D tracking chain for both the Open Data Detector and ATLAS ITk. The improvement of both physics performance, e.g. efficiency and resolution, and computational performance, with 4D measurement compared to traditional 3D measurement will be discussed.