Feasibility Study of the Time Reversal Symmetry Tests in Decay of Metastable Positronium Atoms with the J-PET Detector

Abstract

This article reports on the feasibility of testing of the symmetry under reversal in time in a purely leptonic system constituted by positronium atoms using the J-PET detector. The present state of T symmetry tests is discussed with an emphasis on the scarcely explored sector of leptonic systems. Two possible strategies of searching for manifestations of T violation in non-vanishing angular correlations of final state observables in the decays of metastable triplet states of positronium available with J-PET are proposed and discussed. Results of a pilot measurement with J-PET and assessment of its performance in reconstruction of three-photon decays are shown along with an analysis of its impact on the sensitivity of the detector for the determination of T -violation sensitive observables.

Sensitivity of Discrete Symmetry Tests in the Positronium System with the J-PET Detector

“…In case of operators which are antisymmetric under a given transformation (marked with "-" in the table), expectation value of the operator must vanish if the respective transformation constitutes a good symmetry. Consequently, observation of a non-zero expectation value of such an operator would be an indication of violation of a given discrete symmetry [5,36]. The notion of testing discrete symmetries in the annihilations of ortho-positronium is therefore based on experimental determination of the expectation values of the angular correlation operators listed in Table 1.…”

“…The scope of applications of the detector ranging from medical imaging development to fundamental studies of positronium annihilations (including modes not observed to date such as ortho-positronium (o-Ps) annihilation into 4γ [3]) requires the DAQ system to impose a minimal bias on the spectrum of recorded events [36]. This is achieved with recording of data in a trigger-less mode [32,37] followed by filtering and reconstruction with a dedicated analysis software framework [38][39][40].…”

Testing CPT symmetry in ortho-positronium decays with positronium annihilation tomography

“…To maintain the symmetry of the setup, we did not limit the e + emission direction to any solid angle besides the limits of the chamber. Instead, the positron flight direction was estimated separately for every recorded three-photon event using the position of the 3γ annihilation vertex reconstructed with a novel trilateration-based technique [39,43].…”

“…Data acquisition operates in a triggerless mode [37,38] to minimise the initial sample bias for discrete symmetry tests and searches for rare positronium decays [39]. A detailed description of the J-PET detector can be found in the supplementary material A.…”

“…To maintain the symmetry of the setup, we did not limit the e + emission direction to any solid angle besides the limits of the chamber. Instead, the positron flight direction was estimated separately for every recorded three-photon event using the position of the 3γ annihilation vertex reconstructed with a novel trilateration-based technique [39,43]. Initial identification of o-Ps→3γ event candidates in the J-PET data was based on photon energy deposition measured through time-over-thresholds (TOTs) of pairs of photomultiplier signals recorded at two ends of a scintillator strip for every registered photon interaction [44,45].…”