Performance of Cooled PWO Scintillators With Signal-Sampling Readout

For the investigation of the charmonium spectrum, yet undiscovered charm-meson states and glueballs, the PANDA detector will be employed at the future FAIR facility. PANDA will contain an electromagnetic calorimeter composed of PbWO4 (PWO) crystals that are cooled to -25 degrees C and coupled to large-area avalanche photodiodes or vacuum phototriodes/-tetrodes. The photosensor signals are continuously digitized by sampling analog-to-digital converters (SADCs) and analyzed online in field programmable gate arrays (FPGAs) that are part of the digitizer module to detect hits and extract energy and time information. The online SADC-data processing algorithm was designed, optimized, and implemented in VHDL for a Xilinx FPGA. In order to estimate the performance of the SADC readout of cooled PWO crystals, several measurements with tagged photons in the energy range of 60 MeV-1.4 GeV were performed. The digital readout improves the energy resolution in particular at low photon energies and simultaneously provides a time resolution below 1 ns for an energy deposition above 80 MeV. The successful application of the online data-processing procedure is an essential step toward the development of a trigger-less readout concept of the data acquisition for the PANDA experiment.