Presented at the 5th Jagiellonian Symposium on Advances in Particle Physics and Medicine, Cracow, Poland, June 29–July 7, 2024

The Jagiellonian-Positron Emission Tomography (J-PET) is distinguished by its ability to determine the polarization plane of photons emitted during the positronium annihilation. According to the Standard Model prediction, photon–photon interactions in its final state due to vacuum polarization can mimic CP symmetry violation at a magnitude of approximately 10 which is significantly larger than the predicted value of the order of 10 for weak interactions. Currently, with the help of the J-PET detector, experimental limits on CP symmetry violation in o-Ps decay are set at a precision value of the order of 10. The J-PET detector measures the polarization direction of annihilation photons without a magnetic field and can investigate discrete symmetry by examining non-zero expectation values of symmetry-odd operators, constructed from the momentum and polarization-related vectors of gamma () quanta coming from the o-Ps annihilation. This work focuses on studying the CP symmetry in o-Ps decay and the initial operator plot derived from data collected over 250 days using the J-PET detector. The primary objective of this experiment is to enhance statistical significance in fundamental symmetry studies and refine the precision of CP symmetry tests. The study utilizes the CP symmetry-odd operator ), where and represent the reconstructed polarization-related and momentum vectors of the photons emitted from o-Ps decay.