Systematic Study of Positronium Production Medium in the J-PET Experiment for the CPT Symmetry Test

The Jagiellonian positron emission tomograph (J-PET) is a novel technology employed to detect multiple photons from positronium annihilation. It employs plastic scintillator strips optimized for the detection of photons in the sub-MeV energy range. The experimental setup consists of a positron-emitting source surrounded by chambers coated with porous materials to facilitate positronium formation. Owing to its large geometrical acceptance and high angular resolution, J-PET enables the reconstruction of various kinematic configurations of positronium annihilations, allowing for precise measurements of angular correlations in ortho-positronium decays. The detector has already demonstrated high sensitivity in charge–parity and charge–parity–time symmetry tests based on such correlations. In the present work, we report a systematic study of the effects of non-uniformity in porous materials used for positronium production in the J-PET setup, performed in the context of a charge–parity–time symmetry test. The systematic uncertainty obtained from this study is 0.59 x 10-5, and contributes negligibly to the total uncertainty of the charge–parity–time symmetry test.