Investigation of orthopositronium 3γ-decay using a multidetector spectrometer

Spectra-angular distribution of the orthopositronium 3γ-decay was investigated for the first time in an asymmetric geometry of annihilation, using multidetector spectrometer ARGUS. In order to analyse the experimental data, a method for selection of the three-photon annihilation events and background reduction, built on the well-known algorithm of Dalitz plane, was developed. The experimentally obtained distribution is found to be in a good agreement with prediction of quantum electrodynamics, calculated by the computer Monte-Carlo modelling. The technique realised in this experiment is going to be used for testing quantum electrodynamics of bound state