Particle identification performance of the prototype Aerogel RICH counter for the Belle II experiment

TL;DR

This paper reports on the development and testing of a novel Aerogel RICH counter with HAPDs for particle identification in Belle II, demonstrating high efficiency and radiation resilience in beam tests.

Contribution

Introduction of a new ARICH counter using silica aerogel and HAPDs, with successful beam test validation for Belle II particle ID.

Findings

Achieved 97.4% pion identification efficiency at 3.5 GeV/c

HAPDs maintained high photon detection efficiency after radiation exposure

Beam test results matched design expectations

Abstract

We have developed a new type of particle identification device, called an Aerogel Ring Imaging Cherenkov (ARICH) counter, for the Belle II experiment. It uses silica aerogel tiles as Cherenkov radiators. For detection of Cherenkov photons, Hybrid Avalanche Photo-Detectors (HAPDs) are used. The designed HAPD has a high sensitivity to single photons under a strong magnetic field. We have confirmed that the HAPD provides high efficiency for single-photon detection even after exposure to neutron and gamma-ray radiation that exceeds the levels expected in the 10-year Belle II operation. In order to confirm the basic performance of the ARICH counter system, we carried out a beam test at the DESY using a prototype of the ARICH counter with six HAPD modules. The results are in agreement with our expectations and confirm the suitability of the ARICH counter for the Belle II experiment. Based on the in-beam performance of the device, we expect that the identification efficiency at 3.5 GeV/c is 97.4% and 4.9% for pions and kaons, respectively. This paper summarizes the development of the HAPD for the ARICH and the evaluation of the performance of the prototype ARICH counter built with the final design components.