Speaker
Description
FoCal, a high-granularity forward calorimeter, is one of the ALICE detector upgrade projects for Run 4 at the CERN LHC, scheduled to collect data starting in 2029, after the Long Shutdown 3. The calorimeter has two main subsystems: a highly granular silicon-tungsten electromagnetic calorimeter (FoCal-E), and a conventional sampling hadronic calorimeter (FoCal-H). FoCal is designed to cover a pseudo-rapidity between 3.4 and 5.8.
The electromagnetic calorimeter comprises 20 layers of tungsten absorbers interleaved with silicon detectors. Out of those active layers, 18 have a granularity of 1 cm2 and they consist of silicon pads read out by the HGCROC, the read-out chip developed for the Compact Muon Solenoid (CMS) High Granularity Calorimeter. The read-out chip allows the measurement of the amplitude of the signal, together with the time-of-arrival and time-over-threshold.
The remaining 2 layers consist of high granularity 30x30 um2 monolithic sensors (ALPIDE) developed for the ALICE inner tracker.
The pad layers measure the shower energy and profile, while the pixel layers enable two-photon separation down to a few millimeters, to discriminate between isolated photons and merged showers of photon pairs generated by the decay of neutral pions. The total silicon sensor area for FoCal-E is about 12 m2 with about 150K individual pad channels and about 4 thousand pixel sensors.
In this contribution, we will discuss the development of the front-end electronics and the main results of the test beam campaigns, with a special focus on the electromagnetic calorimeter.
