ARICH for Belle II

Abstract

We report development and current status of Aerogel Ring Imaging Cherenkov counter (ARICH) which is a particle identification detector in the next generation B-factory experiment, the Belle II. The main components of the ARICH are aerogel radiator and photon sensor. When a charged particle goes through the radiator, it emits Cherenkov light photons to the direction which depends on the particle velocity. Combining observables in the Belle II detector, such as a momentum measured with tracker installed inside of the ARICH, and directions of the Cherenkov light photons with the ARICH, we obtain the charged particle mass information. A new photon sensor named Hybrid Avalanche Photon Detector (HAPD) is used to collect a small number of the Cherenkov light photons distributed in the large area effectively. We set up a small part of the ARICH detector and perform the measurement using electron and hadron beam lines at KEK, CERN and DESY. From the obtained results, we expect that it is possible to separate K- and π-mesons by more than 5σ significance level with the ARICH design. The HAPD and its readout electronics production has been started and several kinds of the quality testing for them are ongoing. We also simulate the whole ARICH detector with a GEANT4-based program and expected performance of the particle identification is sufficient for charged tracks in a wide momentum range. After finishing the production of the all components, the construction of the ARICH detector will start in this year and installation to the Belle II detector will be completed in 2015.