Continuous data taking with the upgraded ALICE GEM-TPC

About

During the long shutdown 2 of the LHC, the ALICE Time Projection Chamber (TPC) was upgraded in order to cope with the increased Pb-Pb interaction rate of 50 kHz planned for Run 3. The MWPC-based amplification system was replaced by stack of 4 Gas Electron Multipliers (GEM) foils combining different hole pitch. In addition to a low ion backflow, other key requirements such as energy resolution and operational stability were met. New read-out electronics send the continuous data stream to the new ALICE online computing farm with a rate of 3.5 TByte/s. The detector has been optimised to read all minimum bias Pb-Pb events that the LHC will deliver in the high luminosity heavy-ion era, at the anticipated peak interaction rate of 50 kHz. In August 2020, the TPC was moved back to its designated position at the LHC interaction point 2 and an extensive commissioning program was started. It includes measurements of laser tracks, cosmic particles, and the irradiation of the TPC with an X-ray source and the flushing of the chamber with radioactive Kr to carry out a pad-by-pad gain calibration. During a pilot beam of LHC in 2021 first collision data were taken together with the full ALICE system and in June 2022 first p-p collision data will be recorded up to a rate equal to the load expected at 50 kHz Pb-Pb interactions.

In the seminar the results from the commissioning and first results from colliding beams will be presented.