Measurements and improvements of the response of the $\overline{P}ANDA$-EMC prototype PROTO 60 to high energetic particles and photons in accelerator experiments

The PANDA experiment at FAIR will provide an opportunity to achieve a better understanding of complex hadronic systems. Measurements will be performed with antiprotons using a fixed-target setup. In order to reconstruct most of the reactions, a precise measurement of electromagnetic probes and their energies are crucial. An important and major component of the detector is therefore the electromagnetic calorimeter. Due to the lack of commercial availability of such ambitious, complex and highly specialized detector systems, detailed research and development are nec essary, including prototype development, testing and optimization. The investigation of the response of a homogeneous electromagnetic calorimeter prototype is the main scope of the present thesis. This prototype, called PROTO 60, is composed out of 60 truncated pyramidal shaped PWO-II crystals, cooled down to -25 C and read out with one Large Area Avalanche Photodiode (LAAPDs). The PROTO 60 represents a small section of the central barrel part of the PANDA calorimeter. Its response is being investigated for the first time over an extensive energy range from 52.34 MeV up to 15 GeV within several experiments measuring the response to energy marked photons or positrons at the highest energy, respectively. The study verified the principle detector concept. A linear response was observed. The achieved overall resolution can be parameterized as: sigma/E= sqrt((1,86%/sqrt(E/GeV))^2+(0,25%/(E/GeV))^2+(1,46%)^2) Due to the use of only one single LAAPD per crystal with the effective surface of 1 cm2 and a not linearized light collection within the crystals, these parameters represent an upper performance limit of the final PANDA calorimeter. A detailed GEANT based model of the prototype was developed in order to investigate the calibration based on cosmic radiation or a 150 GeV muon beam and to understand the impact of the detailed geometry and light collection on the achieved performance. Furthermore, the influence of the APD gain on the energy resolution was examined with a light pulser system. The performed measurements revealed that a gain of 50, as used for the CMS electromagnetic calorimeter, does not apply for the PANDA electromagnetic calorimeter in particular in the low energy regime.