The PANDA experiment (antiproton annihilation at Darmstadt) is designed for studies of the strong force in the transition region between perturbative and non-perturbative quantum chromo dynamics (QCD). It will be built and placed at the highenergy storage ring, HESR, at FAIR (Facility for antiproton and ion research) in Darmstadt and start its first experiments in 2025. In the HESR antiprotons with a momentum in the range 1.5 GeV/c to 15 GeV/c will collide with a fixed hydrogen or nuclear target. The PANDA detector is designed for e.g. detailed spectroscopy of hadrons produced in antiproton-proton interactions. In 2026 PANDA will be upgraded with the implementation and completion of some subdetectors, e.g. the EDD (end disc detector of internal reflected Cherenkov light) for charged particle velocity measurements in the forward direction.

This thesis summarizes preparatory experiments with a PANDA forward endcap electromagnetic calorimeter (EMC) prototype, performed at the tagged photon facility at the MAX IV laboratory in Lund to study the response to photons with energies below 100 MeV using vacuum photo tetrodes (VPTTs) as photo sensors. The results show that with VPTT photo sensors, in combination with sampling ADCs, the technical design report (TDR) requirement, with regard to energy resolution, can be fulfilled even for energies below 100 MeV. It is also shown that the energy resolution is not significantly influenced by the insertion of the EDD in front of the forward endcap EMC.