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Abstract

In the upcoming LHC Run 3 the upgraded Time Projection Chamber (TPC) of the ALICE experiment will record Pb--Pb collisions in a continuous readout mode at an interaction rate up to 50 kHz. These conditions will lead to the accumulation of space charge in the detector volume which in turn induces distortions of the electron drift lines of several centimeters that fluctuate in time. This work describes the correction of these distortions via a calibration procedure that uses the information of the Inner Tracking System (ITS), which is located inside, and the Transition Radiation Detector (TRD) and the Time-Of-Flight system (TOF), located around the TPC, respectively.

The required online tracking algorithm for the TRD, which is based on a Kalman filter, is the main result of this work. The procedure matches extrapolated ITS-TPC tracks to TRD space points utilizing GPUs. The new online tracking algorithm has a performance comparable to the one of the offline tracking algorithm used in the Run 1 and 2 for tracks with transverse momenta above 1.5 GeV/c, while it fulfills the computing speed requirements for Run 3. The second part of this work describes the extraction of time-averaged TPC cluster residuals with respect to interpolated ITS-TRD-TOF tracks, in order to create a map of space-charge distortions. Regular updates of the correction map compensate for changes in the TPC conditions. The map is applied in the final reconstruction of the data.