Calibration of aerogel ring-imaging Cherenkov detector in Belle II spectrometerMrvar, Manca (Avtor) Pestotnik, Rok (Mentor) The Belle II spectrometercalibrationCherenkov photonsthe charged kaon/pion separationhybrid avalanche photodetectorparticle identificationRing-Imaging Cherenkov detector.The Aerogel Ring-Imaging Cherenkov detector (ARICH) provides a charged particle identification in the endcap region of the Belle II spectrometer at the SuperKEKB asymmetric-energy $e^+ e^−$ collider in Tsukuba, Japan. The ARICH consists of a double layer aerogel radiator in a focusing configuration, an expansion volume and a plane of hybrid avalanche photodetectors. The methods of the calibration of the photodetectors and the readout electronics are discussed in the dissertation. The hardware calibration improved the separation of charged kaons and pions, which was studied with the $D^{*+} \to D^0 (\to K^- \pi^+) \pi_s^+$ decay. The identification algorithm was tested on the simulated sample. The simulation results show the efficiency of kaon identification above 90 percent at the pion misidentification probability of 5 percent. The developed procedure was also applied on the sample of collision data that was collected during the detector commissioning phase. Due to limited sample of the measured data, only the reconstructed $D^0 \to K^- \pi^+$ events were used for the performance studies. The results provide slightly decreased performance due to incomplete calibration of the tracking and particle identification system at the beginning of the operation.20192019-01-30 11:34:07Doktorsko delo/naloga106124sl