Study of monitoring system of a calibration laser for the iTOP detector at Belle II

The work presented in this thesis concerns a study on a calibration system to be used by the iTOP (”Time Of Propagation”) detector in the Belle II experiment at superKEKB, managed by KEK, the Japanese High-Energy Accelerator Research Organization. The iTOP detector will be used to identify charged particles, π and K. A calibration system for the iTOP uses a laser, whose characteristic emission is to be known. The thesis focuses on the developement of a data analysis method to be used in the monitoring system to describe the emission and study its behaviour under different conditions. The signal acquired is described as a RC decay: an estimate of the pedestal value is computed, and the distribution of the delay between the trigger pulse and the arrival of the photon is discussed. Different variables is considered: the maximum amplitude of the signal, the amplitude at a fixed bin, and the integral of the signal. Furthermore, the signals are fitted: the distribution of the parameters allows a deeper inspection, while the integral of the function is taken into account as a descriptive variable. The best variable results to be the integral of the signal, which presents a neatly separated distribution, well described by a sum of Gaussian functions. Since this method is tested with different settings of the laser, it is ready to be used to analyze a variety of working conditions.