A method for selecting three-photon positronium-annihilation events with a multidetector coincidence spectrometer

A method for event selection takes into account all features of orthopositronium-atom annihilation. The spectral and angular distributions of positronium three-photon decay was investigated with the 4π-spectrometer ARGUS. The filtration program for the events corresponding to the three-photon positronium decay was developed, and positronium 3γ-annihilation was simulated by the Monte Carlo method. The measured spectra agree well with the simulation. The technique developed will be used to test the quantum electrodynamics of bound state.