The Belle II experiment is a new generation B factory experiment at the SuperKEKB electron-positron collider. The main purpose of the experiment is to search for new physics with a huge sample of B meson decays. The proximity-focusing Aerogel Ring-Imaging Cherenkov detector (ARICH) has been designed to identify kaons and pions in the forward end-cap of the Belle II spectrometer. Using aerogel as radiators with a specialized photon sensor called HAPD, the K/π separation is expected to reach more than 4 σ in the momentum range of 0.5 to 4.0 GeV/c.
ARICH was constructed in summer 2017 and was installed in the Belle II spectrometer in the beam line of SuperKEKB collider. The test of ARICH is performed using both cosmic rays and the beam collision during the accelerator commissioning. We observe Cherenkov rings in ARICH associated with charged tracks detected by the tracking system.
Different ARICH parameters including the number of Cherenkov photons per charged track and Cherenkov angle distribution of detected photons are evaluated for both data sets and compared to expected values obtained by simulation. Preliminary results of the cosmic ray data analysis showed good agreement with the expected values and the results for all the data collected during commissioning of the detector will be presented. We also discuss detector parameters that are a part of the data quality monitoring system evaluating the detector performance during data-taking.
Particle identification capability based on likelihood calculation was also studied with the beam data and compared with the simulation for each particle species, especially for kaons and pions to evaluate K/π separation of ARICH. The results of this study will also be reported.