Operation and Performance of Belle II Aerogel RICH Counter

The Belle II experiment at the SuperKEKB aims collecting 50 times more data than its predecessor Belle. One of key components in is particle identification (PID), especially separation kaons and pions. In spectrometer, a proximity focusing ring imaging Cherenkov detector using aerogel as radiator (ARICH) equipped for PID forward endcap. this counter, total 420 hybrid avalanche photo-detectors (HAPDs) with 144 channels are used position-sensitive photon detectors that work inside 1.5 T magnetic field. started physics run full from 2019. We report on operation ARICH, including fraction dead channels, stability HAPDs, encountered problems. also performance ARICH estimated D * + → 0 π slow , D 0 → K − π + control sample initial data.