In our universe, we observe asymmetry between the matter and antimatter. In 1967 A. Sahkarov proposed a solution requiring, among others, the existence of CP symmetry violation (C - charge conjugation, P - parity). This was indeed observed in the quark sector but at the magnitude which is not large enough to solve the matter-antimatter asymmetry problem. Since the CP violation is allowed by some leptogenesis models, the search for additional CP symmetry violation was extended to leptonic sector. A recent experiment involving neutrino oscillations reported the indication of CP violation but with no decisive conclusion.
A complementary approach is to use the decay of Ortho-Positronium (o-Ps), which decays into three gammas. o-Ps has well-defined C, P and T (T - time reversal) properties, what makes it suitable to probe for the violation of individual symmetries and their combinations (CP and CPT) which are related to a particular angular correlation between the direction of the Positronium spin and the momenta of gammas. Any deviation of the angular correlation amplitudes from zero would indicate discovery of a new physics.
Within this action we will build a new experimental set-up and perform measurement of CP and improve the precision level compared to the state-of-art results. The key part of the experimental set-up will be a ring of detectors consisting of 24 BaF2 crystals for detection of 3 gammas. The data acquisition system will be based on fast pulse digitizers, what will increase the rate and the amount of collected data but will also increase the complexity of the data analysis. Data collected in this measurement will also contain information on two CPT amplitudes. We will determine both, and one of them will be determined for the first time. Since no suitable polarimeter for annihilation gamma rays exists at the moment, we will study polarization sensitivity of a single-layer Compton polarimeter based on 8x8 GaGG(Ce) crystal array, which will be read out by a matching SiPM array.
