Studies of Ortho-Positronium Decays into Three Photons with the J-PET Detector

A. Gajos on behalf of the J-PET collaboration Institute of Physics, Jagiellonian University, S. Łojasiewicza 11, 30-348 Cracow, Poland

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The Jagiellonian Positron Emission Tomograph (J-PET) setup, besides being the first PET scanner built with plastic scintillators is currently used to conduct a broad range of experiments involving ortho-positronium (o-Ps) decays into three photons. We present results of studies of o-Ps→3γ decays performed in J-PET with a view to search for angular correlations between the photons' momenta and positronium spin direction which would violate the combined CPT symmetry, scarcely tested in leptonic systems. To date, the most precise CPT test using ortho-positronium decays reached the precision of 3×10-3 whereas effects limiting the sensitivity are only expected at the level of 10-9. In the discussed J-PET measurement, ortho-positronium atoms are created by positrons from a 22Na source thermalizing in an extensive-size cylindrical target of mesoporous silica and decay positions are reconstructed using a trilateration-based technique. Decay photons are recorded by 192 strips of plastic scintillators with high timing resolution. Such a setup allows for registration of an unprecedented spectrum of geometrical configurations of o-Ps→3γ decays including also correlations with positronium spin. With an angular resolution and o-Ps polarization control improved with respect to previous measurements, J-PET aims at achieving the sensitivity of CPT test at a precision level of at least 10-4.

DOI:10.12693/APhysPolA.137.126 PACS numbers: 11.30.Er, 36.10.Dr, 13.40.Hq