Studies of PWO Crystals and Simulations of the p̅p →Λ̅Λ, Λ̅Σ0 Reactions for the PANDA Experiment

Abstract: The thesis comprises investigations of two topics related to the PANDA experiment. The first part is dedicated to energy resolution and light yield uniformity studies of PWO crystals for the electromagnetic calorimeter. The second part of the thesis is dedicated to simulation studies of the p̅p→Λ̅Λ and the p̅p→Λ̅Σ0 channels.Photon response measurements with one 3×3 crystals matrix of rectangular crystals and one 5×5 matrix with tapered crystals have been performed at the MAX-Lab synchrotron facility in Lund, Sweden. Photon energies in the range of 13-84 MeV were used. GEANT4 simulations were performed in order to find the most suitable method for adding the energy contributions and for calibration purposes. The widths, σ, of the resulting experimental summed energy peaks were fitted using the Novosibirsk distribution. The results show that the electromagnetic shower at 84 MeV is completely contained in the 5×5 matrix. The widths (σ) for the summed energy peaks were determined.Studies of the uniformity of the light yield were performed for crystals of three different shapes and different wrapping materials. The light yield as a function of distance between the point of energy depositions and the PM tube, was shown to be closely related to the crystal shape and the wrapping material.The p̅p→Λ̅Λ channel was studies at beam momenta of 1.64 GeV/c, 4 GeV/c and 15 GeV/c, while p̅p→Λ̅Σ0 was studied at 4 GeV/c. In the simulations, both phase space differential cross-sections and experimental differential cross-sections from PS185 were used as input. The purpose of the simulations was to show that the reaction channels can be reconstructed in the detector. Special interest was paid to the polarisation and spin correlations of the hyperons. The result is that there is acceptance of cosθ angular range over the full momentum range of the HESR for both channels. Using isotropic differential cross-sections, the polarisation for Λ̅ and Σ0 as well as spin correlations between Λ̅Λ and Λ̅Σ0 can be well reconstructed. Using the differential cross-sections from PS185, the particles are more likely to go forwards in their respective directions in the CM-system, thus making reconstruction over the full angular range more difficult at high beam momenta.