Kenta Uno

01 January 2022

Abstract: The Belle II experiment at the SuperKEKB asymmetric-energy $e^{+}e^{-}$ collider is a B factory experiment to search for new phenomena beyond the Standard Model. One of the most important point in the experiment is a particle identification, especially the separation between kaons and pions. Thus, a proximity focusing Aerogel Ring Imaging Cherenkov~(ARICH) counter is implemented in the forward endcap region to distinguish kaons and pions with momenta up to 4~GeV/$c$. The ARICH counter consists of a silica aerogel radiator and Hybrid Avalanche Photo Detector~(HAPD). When a charged particle traverses the radiator, Cherenkov photons are emitted in the radiator and the emitted photons are detected by the HAPDs. The Belle II experiment started the physics run in 2019 and accumulated 424 fb$^{-1}$ of collision data. The ARICH counter has been stably and the performance is consistent with our expectations. We report the detail of the operation of HAPDs and readout electronics. We also report the performance of ARICH counter using the data.

Keyword(s): ARICH counter, particle identification, photon detector