Speaker
Description
First studies of discrete symmetries in purely leptonic systems started several decades ago and led to the discovery of weak interactions. Nowadays a positronium is considered as a fine probe into this subject, due to the fact that it is the lightest matter-antimatter system and at the same time an eigenstate of the C and P operators.
The Jagiellonian Positron Emission Tomography (J-PET) collaboration works on developing its new experimental program focusing on using large-acceptance detector of gamma quanta originating from positronium decays [1,2]. The experimental apparatus consists of 192 plastic scintillators read out from both ends with vacuum tube photomultipliers. Signals produced by photomultipliers are probed at four levels [3] in the amplitude domain and digitized on 8 FPGA based readout boards in triggerless mode [4]. In order to The energy deposition inside detection modules is determined based on the TOT (Time Over Threshold) response. Using the TOT technique, as a measure of energy loss instead of charge integration methods, significantly reduces system deadtime. This is especially crucial in case of J-PET, built out of plastic scintillators producing very fast light pulses. The drawback in adopting this technique lies in the non-linear correlation between input energy loss and TOT of the signal, which has been already characterised [5]. Additionally whole system calibration can be performed on the same data which is used to study discrete symmetries [6] which increases time which can be delegated to proper data taking.
It was observed experimentally that C-symmetry is violated in weak interactions and the best limit of the C symmetry violation in the electromagnetic interaction was set with the π0 → 3γ decays which amounts to branching ratio of (3γ/2γ) equal to 3.1 × 10−8 at 90% C.L [7]. Experimental test of C-symmetry in positronium decays was performed by Mills and Berko (1967) [8] and the best limit was set for 1^S_0 → 3γ which amounted to 2.6 × 10−6 at 68% C.L.
In the scope of this presentation a description of measurements performed in order to test C-symmetry [9] will be discussed and initial results from the studies performed with J-PET detector with small detection chamber will be shown.
Bibliography:
1. S. Niedźwiecki, et al., Acta Phys. Pol. B 48, 1567 (2017).
2. P. Moskal, et al. Nature Rev. Phys., 1, 527 (2019).
3. N. Sharma et al., IEEE Trans. on Rad. and Plas. Med. Scien., Vol. 4, No. 5, 528 (2020) .
4. S. Sharma et al., EJNMMI Phys 7, 39 (2020).
5. G. Korcyl et al., IEEE Trans. On Med. Imag. Vol. 37, No. 11, 2526 (2018).
6. K. Dulski et al., Acta Phys. Pol. B 51, 195 (2020).
7. P. Moskal, et al., Acta Phys. Pol. B 47, 509 (2016).
8. A. P. Mills and S. Berko, Phys. Rev. Lett. 18, 420 (1967).
9. S. D. Bass, Acta Phys. Pol. B 50, 7 (2019).
| Collaboration | J-PET group |
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