Speaker
Description
The LHCb RICH system comprises two detectors, delivering excellent charged-hadron discrimination across the momentum ranges 2.6-60 GeV and 20-100 GeV respectively. Following its 2022 upgrade, the system employs more than 3000 Multi-anode Photomultiplier Tubes (MaPMTs) and operates at the full 40 MHz LHC bunch-crossing rate. Each of the 64 anodes of an MaPMT is digitised by a CLARO channel, giving $2\times10^5$ pixels that require careful gain and threshold calibration. With a recovery time below 25ns per channel, the RICH maintains peak pixel occupancies below ~30%, even in its busiest regions. This contribution details the characterisation and performance of the MaPMT technology after three years of operations in the LHCb experiment. Dedicated quality-assurance studies have fully characterised the signal-induced noise (SIN) of the MaPMTs, leading to HV and timing profiles that define the configurations and time-gating strategies used to mitigate SIN. Regular calibration scans further counteract ageing effects from the high-photocurrent environment by reconfiguring gain and threshold on a per-channel basis. In addition, detailed surveys have characterised the relative detection efficiency across the RICH surfaces using the full luminosity integrated by LHCb. The results of these efforts, and more, are described herein. Furthermore, the MaPMTs have allowed the RICH system to provide a new measurement of instantaneous luminosity to operate LHCb: the details of such technique will be presented as well.
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