Angular correlations between electrons and photons in the electron excitation of helium and neon

Angular correlations have been measured between the electrons exciting the 21P state in helium and the photons arising from the decay of this state to the ground state. Analysis of these angular correlations yield the ratio γ of the differential cross sections for the excitation of the m=1 and m=0 magnetic substates, and the relative phase chi of the scattering amplitudes for the excitation of these substates. The parameters γ and chi have been measured at 80 eV and 120 eV and scattering angles between 100 and 160. The data are compared with the predictions of the first Born approximation and the Glauber approximation which show relatively good agreement for γ but poor agreement for the relative phase chi. Where the present data overlap with previous measurements excellent agreement is found. Data are presented for the parameters γ and chi for the excitation of the resonant 31P1 state in neon. (author)