CPT symmetry test in positronium annihilations with the J-PET detector

Abstract

Discrete symmetry under combined transformation of charge, parity and time reversal (CPT) can be tested in the decays of positronium atom, the lightest bound system built of charged leptons. Jagiellonian Positron Emission Tomograph (J-PET) device constructed from plastic scintillators, detects the photons originating from electron positron annihilation. This feature enables J-PET to study CPT symmetry in the three photon annihilations of the triplet state of positronium. Signs of violation of the CPT symmetry can be sought as a non-vanishing expectation value of an angular correlation operator that is odd under CPT transformation. A technique to estimate the spin of ortho-positronium and momenta of annihilation photons for single recorded ortho-positronium annihilation events allows J-PET to measure the expectation value of a CPT symmetry odd angular correlation operator. J-PET measures a broad range of kinematical configurations of ortho-positronium annihilation to three photons and is the first experiment to determine the full range of the CPT-odd angular correlation.

CP symmetry test at J-PET

“…This yields 384 analog channels, which are processed by a fully equipped trigger-less Data Acquisition System (DAQ) and readout mechanism [17][18][19]. The experiments were conducted with a point-like 22 Na source placed in the center of the detector and surrounded by a porous polymer [20,21]. The positrons emitted from the source ( 22 𝑁𝑎 → 22 𝑁𝑒 * + 𝑒 + + v 𝑒 ) combine with the electrons in the porous polymer to produce ortho-Positronium (o-Ps), a meta-stable triplet state that primarily decays into three photons due to charge conjugation symmetry conservation.…”

“…The periods devoted to measurements for CPT symmetry studies last from 26 days [5] up to 9 months, being 16 months in total, while measurements for CP symmetry last from 6 days up to 8 months (12 months in total). It is worth to mention that new data-taking campaigns using modular version of J-PET detector are in progress now, with the aim to improve the already published result [22].…”

Testing Discrete Symmetries in Ortho-Positronium Decays with the J-PET Detector

“…It is worth mentioning that new data-taking campaigns using a modular version of the J-PET detector are scheduled already, with the aim to improve the already published result. 14…”