The hadron collider LHC ended its second period of data taking at the end of 2018 after a successful three-year run (2015:2018 Run 2). Since then, during the shutdown of the world largest particle accelerator several important upgrade of the accelerator complex and of the detectors have been carried out. Obviously also these operations were slowed down by the pandemic due to Sars-Cov-2 virus and consequent restrictions.

The time of flight (TOF) detector of the ALICE experiment has been built under leadership of ALICE group in Bologna. Since July the TOF ALICE group completed upgrades of the readout electronics. They included the production of a new readout card, designed by INFN Bologna, that houses high-speed optical links.

The TOF detector was gradually turned on during Summer. After many commissioning operations, the group has completed this week a first data taking observing the time-of-flight of the muons. These are particles produced by the interaction of cosmic rays with the atmosphere nuclei and able to cross two opposite modules of the TOF at a distance of around 8 meters. In the figure it is reported the difference between the time-of-flight measured and the expected one, based on the distance between the two channels hit on the detector.

At the LHC particle beams (and collisions) are foreseen to restart only since February 2020. During commissioning phase it is standard practice to use these particles coming from cosmic rays. Among the many sub-systems in ALICE currently completing their upgrade programme, the TOF is the first detector, with upgraded electronics, already restarting such measures, finally observing again particles inside the detector!

The TOF team was able to perform the measurement controlling remotely all the operations, with personnel connected from Bologna and CERN offices, or from private homes, but no presence was required at the experimental site in Saint-Genis-Pouilly where the ALICE experiment is.