Studies of CPT symmetry in positronium decays with 192 plastic strip J-PET detector

Abstract

A direct test of the CPT symmetry is performed for the electromagnetic decays of ortho-positronium using the J-PET tomograph. We present the precise measurement of the CPT-sensitive angular correlation entailing the positronium spin and the momenta of its annihilation photons, surpassing previous studies utilizing the same detection system. Positrons originating from a $^{22}$Na source are emitted from the detector's center and subsequently form positronium atoms within the spherical chamber covered with porous material. Reconstruction of annihilation locations using the 192-strip J-PET detector makes it possible to determine the positronium emission direction, which defines the quantization axis along which positronium is polarized, without the application of external magnetic fields. The measurements were performed in total for 356 days resulting in an identification of 47.8 million events with ortho-positronium decays into three photons. The results are consistent with the exactness of CPT symmetry with measured asymmetry amplitude -0.00029 $\pm$ 0.00022 (stat.) and with statistical error four times smaller than the previous best measurement.