Electron-proton angular correlation measurements for the 21P state of helium

Electron-photon angular correlations have been measured by detecting, in delayed coincidence, electrons inelastically scattered from helium and photons emitted in decays from 21P state at incident electron energies of 60 to 80 eV. Analysis of the data yields values for the ratio lambda of the differential cross sections for magnetic sublevel excitations and the phase difference mod chi mod between the corresponding probability amplitudes. The measurements extend over the angular range 10-120 degrees of electron scattering angles. The present data are in good agreement with the experimental results of Hollywood et al. (1979) and show a marked discrepancy at large scattering angles with the recent data of Steph and Golden (1980). The experimental results are compared with some recent theories.