Calibration of the Belle II aerogel ring imaging detector

For efficient separation of hadrons in the forward end-cap of the Belle II spectrometer, an aerogel proximity focusing Ring Imaging Detector is installed in the high magnetic field between the central drift chamber and electromagnetic calorimeter. Cherenkov photons, emitted in the double layer aerogel radiator are expanded through the empty space and detected on the photon detector consisting of Hybrid Avalanche Photo diodes. The readout electronics working in a threshold mode records hit patterns registered during beam collisions. A particle identification algorithm based on the two dimensional extended maximum likelihood technique is used to assign probabilities for different particle hypotheses of tracks traversing the aerogel RICH detector. For efficient discrimination, the Aerogel RICH detector has to be calibrated. We present the key calibration steps used to optimize the detector performance.