Two-Photon Decay of Para-Positronium Within a Composite Approach

M. Piotrowskaa, F. Giacosaa, b aInstitute of Physics, Jan Kochanowski University, ul. Uniwersytecka 7, 25-406 Kielce, Poland bInstitute for Theoretical Physics, J.W. Goethe University, Max-von-Laue-Str. 1, 60438 Frankfurt, Germany

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The decay of the para-positronium into two photons is studied in the framework of a composite quantum field theoretical approach. This amounts to the evaluation of the electron-positron dressing, the Weinberg compositeness condition for the positronium, and the triangle-shaped diagram with virtual electrons circulating in it, leading to the final two-photon state. An important role is played by the positronium-electron-positron vertex, which is linked to the wave function of the para-positronium. We show how possible choices for the vertex function affect the γγ decay rate. Outlooks to other decay channels and other positronia are presented.

DOI:10.12693/APhysPolA.146.699 topics: positronium, compositeness condition, vertex function