Response of the PANDA electromagnetic calorimeter to photons with energies below 100 MeV

Sammanfattning: Characteristics of the electromagnetic calorimeter of PANDA (anti-Proton ANnihilations at DArmstadt), one of the key experiments at FAIR, have been measured at the tagged photon beam facility at MAX-lab for 61 energies in the range 12-63 MeV. The tested detector array consisted of 5x5 PbWO4 (lead tungstate) crystals designed for the forward end-cap. The array was cooled to -25 ºC and read out with conventional photomultiplier tubes. The measured energy resolution, ?/E, (for example 6 % at 20 MeV) shows that the current design meets the criterion of PANDA. The array is now ready to be equipped with vacuum phototriods designed for the forward end-cap.       As a part of the experiment, characteristics of the tagging spectrometer at MAX-lab were measured. This revealed a lowered performance in terms of resolution for low energies. A discrepancy between the nominal and the measured tagged energies was also discovered. Possible explanations to these observations are presented.