Faculty of Physics, Astronomy
and Applied Computer Science

Positronium (Ps) is an exotic atom composed of an electron and its antiparticle, the positron, bound together in a short-lived quantum system. This bound state serves as a unique system for probing fundamental physics, as its properties are precisely predicted by Quantum Electrodynamics (QED) within the Standard Model (SM). Furthermore, its decay processes, which are effectively modeled using Monte Carlo simulations, provide valuable information on various domains of particle physics. At the Jagiellonian University, the J-PET detector (Jagiellonian Positron Emission Tomograph), a novel tomography system based on plastic scintillator detectors, has been developed. This setup offers high angular and timing resolutions, enabling multidisciplinary studies of positronium decays. Therefore, it is possible to measure the lifetime of positronium with high precision with J-PET. In this work, we report on ongoing searches for Dark Matter signatures in ortho-positronium (o-Ps) decays using the J-PET detector. The primary objective is to explore the existence of Mirror Matter, a hypothetical form of matter proposed to restore parity symmetry and considered a plausible candidate for the Dark Matter component of the Universe. Our study aims to refine current experimental limits by achieving high-precision measurements of the o-Ps lifetime in its three-photon decay channel, comparing these results with QED predictions to search for potential deviations that could be interpreted as a signal of the presence of Dark Matter.

Positronium (Ps), an atom made of an electron and a positron, is a sensitive system for testing Quantum Electrodynamics (QED) and searching for physics beyond the Standard Model, including dark matter candidates like mirror matter. Some theories predict that ortho-positronium (o-Ps) can oscillate into invisible mirror states, altering its lifetime. We investigate this with the Jagiellonian Positron Emission Tomograph (J-PET), a high-resolution detector based on plastic scintillators and SiPM readout. Experiments are performed in vacuum with XAD4 porous polymer to boost positronium formation. Using Monte Carlo simulations, advanced event reconstruction, and background suppression, we isolate three-photon o-Ps decays and measure lifetimes with high precision. Our aim is to reach $10^{-6}$ sensitivity, enabling stringent QED tests and indirect searches for mirror matter, thereby constraining hidden-sector models and informing dark matter research.

Quantitative accuracy in Positron Emission Tomography (PET) depends on reliable attenuation correction (AC) methods, and novel imaging concepts such as positronium lifetime imaging with the Jagiellonian PET (J-PET) system have further highlighted the importance of developing advanced PET methodologies. The clinical standard for AC in PET imaging remains computed tomography (CT). However, this approach increases patient radiation dose and imaging expenses. In recent years, several CT-less attenuation correction methodologies have been proposed to eliminate the need for CT scans. In this work, we present a feasibility study for a CT-less AC approach that utilizes photons undergoing Compton scattering within the PET detector?data typically discarded in conventional analyses. This method is especially well-suited to the J-PET scanner, which is built from long plastic scintillators that inherently produce a significant number of detectable scattered photons. We performed simulations using the GEANT4 Application for Tomographic Emission (GATE) [6] by modeling a modular J-PET scanner with phantoms having varying attenuation profiles. We then analyzed the Lines of Response (LORs) formed between the first interaction at the detector and the subsequent detection of the scattered photon after it passes through the phantom and reaches the detector on the opposite side. Our initial findings show that these LORs contain spatial information about the phantom's attenuation distribution, enabling the distinction between varying attenuation density regions. These results demonstrate that detector-scattered photons can serve as an intrinsic data source for generating attenuation maps.