Abstract
ALICE is the dedicated heavy-ion experiment at the CERN Large Hadron Collider (LHC). Its main tracking and particle-identification detector is a large volume Time Projection Chamber (TPC). The TPC has been designed to perform well in the high-track density environment created in high-energy heavy-ion collisions. In this proceeding, we describe the track reconstruction procedure in ALICE. In particular, we focus on the two main challenges that were faced during the Run 2 data-taking period (2015–2018) of the LHC, which were the baseline fluctuations and the local space charge distortions in the TPC. We present the corresponding solutions in detail and describe the software tools that allowed us to circumvent these challenges.
Highlights
ALICE was designed to cope with about 20,000 charged primary and secondary tracks √emerging in the Time Projection Chamber (TPC) acceptance (|η | < 0.9) from central Pb–Pb collisions at sNN = 5.5 TeV.Such high-track densities are achieved in pp collisions collected at high interaction rates, which cause pileups of particles from several collisions in the TPC drift time
We will focus on the so-called combined tracking procedure, which uses the central barrel detectors; the Inner Tracking System (ITS), the Time Projection
The vertex constraint significantly improves the resolution of TPC standalone tracks, while it has no effect on ITS–TPC tracks
Summary
ALICE was designed to cope with about 20,000 charged primary and secondary tracks. emerging in the TPC acceptance (|η | < 0.9) from central Pb–Pb collisions at sNN = 5.5 TeV. The improvement in pT resolution after applying a vertex constraint and including the TRD in the track fitting are shown in the left and right panels of Figure 2, respectively. The vertex constraint significantly improves the resolution of TPC standalone tracks, while it has no effect on ITS–TPC tracks (green and blue square overlap). For Improvement of the q_pT TPC resolution in data when TRD information is included as vertex. Collisions standalone and matched tracks compared with the performance of tracking without TRD information for various running it has no effect (green and blue squares overlap). Typical width of the tracklet-to-track residuals in y observed during the internal alignment interaction rates of(IR) It provides the best estimate trackof parameters, global track reconstruction (defined by the remaining chambers of the stack). This is essential for a reliable and fast-turnaround optimization
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