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

Positronium (Ps), governed by Quantum Electrodynamics (QED), provides a rich domain for exploring fundamental physics. Monte Carlo simulations of its decay provide insights into various aspects of particle physics. The development of J-PET, an innovative tomography system at the Jagiellonian University using high-resolution scintillator detectors, facilitates interdisciplinary studies encompassing fundamental physics tests, medical research, and quantum entanglement measurements but also enhances our capacity to investigate positronium decays in pursuit of potential dark matter (DM) candidates, a lingering enigma within the current Standard Model (SM) framework. In our research, we employ the J-PET detector to study ortho-positronium (o-Ps) decays as a part of our ongoing quest for the discovery of DM. Our primary goal is to explore mirror matter, which seeks to restore parity invariance and is proposed as a candidate for the Universe’s DM. Our study aims to push the boundaries of precision measurement in the decay width of o-Ps to three gamma quanta, contributing to our understanding of the elusive nature of dark matter. The article presents the preliminary lifetime distribution of o-Ps as a search for mirror matter obtained from data collected during a portion of a long-term measurement conducted with the J-PET detector in 2020. The long-term aim of the study is to achieve 10 lifetime sensitivity.