Dynamics of Internally Converted Electron-Positron Pairs

The reactions studied were π^-+p→n+π⁰ (π⁰→γ+e⁺+e^-) and π^-+p→n+e⁺+e^-. From a sample of {~}15 000 internally converted electron-positron pairs, 7000 were measured, of which 4200 were used in the detailed analysis. The differential distributions in y (the energy partition) and x² (the virtual mass of the photon) agree with the theoretical quantum electrodynamic calculations. A measure of the form factor for the π⁰→2γ reaction gave a value Γ(xμ)=1-(0.24±0.16)x²μ², where μ is the mass of the pion. It was further demonstrated that the number of events necessary to determine the contribution of the longitudinally polarized virtual γ rays in the second reaction is of the order of 50 times that in the present experiment.