Performance study of the FoCal prototype detector using a 2.0 - 5.4 GeV pure positron beam

Abstract

This research commenced by preparing the Forward Calorimeter (FoCal) prototype detector for measurements on a 2.0 - 5.4 GeV pure positron beam at DESY, Hamburg. At beam energies of 2.0, 3.0, 4.0, and 5.4 GeV, enough data has been collected to achieve reasonable statistics. Additionally, data with 3 different threshold settings for the sensors has been collected at 2 GeV. During the first analysis of the data it was found that series of neighboring pixels in the sensors seemingly randomly turned on in multiple frames. Because of this effect (and other problems, such as synchronization errors), the detector has an undesired instability in time. The first part of this thesis is focused on the investigation of said problems. The sections in the sensors that were found to have complications, have been masked in further analysis. In the second part, the energy resolution, longitudinal profile and linearity of the detector were checked to quantify the effects of the masking procedure. It was found that the energy resolution got worse for the 2.0 , 3.0 and 4.0 GeV data, but improved for the 5.4 GeV data. The linearity of the detector was found to be better with the masked data. Furthermore, the influence of the threshold settings has been determined. It was found that the low-threshold settings had the best energy resolution and the highest clustersize; the high-threshold settings had the highest signal-to-noise ratio. There are still multiple problems with the hardware, such as hot channels, synchronization errors and an inefficiency in the trigger system, that have not been dealt with in this work.