Ortho-positronium decay and the search for CP and CPT violation in leptonic sector

In the nature, we observe disbalance between the matter and antimatter, which can be explained by requiring of CP symmetry breaking.

This was already observed in the quark sector, but the level of violation was not enough to explain the matter-antimatter asymmetry. Recent experiment involving neutrino oscillations reported the indication of CP violation in the leptonic sector.

Ortho-Positronium (spin 1), a purely leptonic system, has very well-defined C and P properties, what makes it suitable for probing the CP ant CPT symmetries by constructing angular correlations between the polarization direction of positronium spin and the momentum or the polarization vector one of 3 gammas.

Any deviation of the angular correlation amplitudes from zero would indicate discovery of a new physics.

Within this action we propose to perform high precision measurement of CP amplitude and improve the precision level for one order of magnitude compared to the state-of-art results.

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.