Construction of a lead fluoride crystal calorimeter for a parity violating electron scattering experiment

In the context of this thesis the highly transparent Cherenkov material lead fluoride (PbF2) has been examined for its suitability as a calorimetric detector. These studies were dominated by systematic quality controls of PbF2 monocrystals concerning their light yield and radiation resistance as well as their transmittance and its homogeneity. Besides, a simulation of the intensity and the spatial distribution of Cherenkov photons in PbF2 as well as model parameterisations are presented. With their help the detectors were optimised for their application in a calorimeter. The homogeneous electromagnetic calorimeter has been constructed in the following years. In this thesis the design features and the completed set-up are shown. Each of the 640 detectors consists of a PbF2 crystal wrapped in reflective material, a photomultiplier with its base and a coupled fibre. Substantial difficulties for the construction resulted from fluctuations in the mechanical dimensions of the crystals of up to ± 500 μm. In order to be able to reject crystals with unsatisfactory geometry, all crystals were measured with a computer-controlled milling machine to an accuracy of 12 μm. The determined characteristics of the crystals are presented in this thesis. In 2000 the first 511 channels of the calorimeter were taken into operation. To achieve stable pulse heights the successfully applied method of optical bleaching was implemented in the calorimeter. The mean energy resolution ΔE/E of the central channels amounted to 4.27%, corresponding to a statistical term σ/ E of (3.1 ± 0.3)% / E [GeV]. After the separation of inelastic scattering events and of pile up a raw asymmetry A = (+3.0 ± 3.0) x 10-6, averaged over all central detectors, was determined from the first measurements. (orig.)