Electron-photon angular correlation measurements for the2P11state of helium

Electron-photon angular correlation measurements have been made for scattered electrons which have excited the $2{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ state of helium and photons from the $2{}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}\to 1{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ transition at an incident electron energy of 80 eV for a range of electron scattering angles ${\theta }_e$ from 5° to 155° and for a photon angle ${\theta }_{\gamma }$ of 90° in the scattering plane. These measurements have been analyzed to obtain relative values of the ratio $\lambda$ of the differential cross section for exciting the $m_j=0\mathrm{}$ sublevel ${\sigma }_0$ to the total differential excitation cross section $\sigma$, for $J=1\mathrm{}$ ($\lambda =\frac{{\sigma }_0}{\sigma }$). The results extend the measurement range to both larger and smaller values of ${\theta }_e$ at this energy and are consistent with previous measurements and the most recent calculation for the process.