Lagrange, Simon ; Taras, Paul

2016
Universite de Montreal Montreal

Abstract: The goal of this work is to optimize the digital processing of signals generated in CsI crystal of an electromagnetic calorimeter in the context of high counting rate experiments like Belle II. The scintillation from the crystal is converted into an electronic signal by a Hamamatsu photopentode with a gain of 150+-2 electrons per photoelectron, then amplified by a preamplifier. The signal is shaped by a shaper, a CR-(RC)^4 active filter before digitized by an ADC, to be processed by the digital signal processing (DSP). Using reference shapes, the DSP can extract the energy deposited by an incident particle and its time of occurrence in the crystal. Three different approaches were used to determine the reference shapes: experimental average shapes, the analytical function for an active filter and the sum of three Gaussian functions. The best results were obtained with the last approach, both with a pulse generator and a CsI crystal. A conversion relation has also been established to convert the measured signal's amplitude into a deposited energy in the crystal. We observed average propagation times of the scintillation through the crystal of 47+-4 ns and 3.4+-0.5 microsec corresponding to the two accessible excited states in the CsI atoms. The crystal geometry, the scattering of photons by its surface and the electronic circuits all contribute to making the scintillation times seem to be longer than they really are.

Note: Presented on 05 11 2016
Note: MSc