Large-angle electron-photon coincidence experiment in atomic hydrogen

Abstract

$1s\ensuremath{-}2p$ excitation in hydrogen has been studied by observing the angular correlation of Lyman $\ensuremath{\alpha}$ photons detected in coincidence with inelastically scattered electrons at 54.4 eV incident energy. The electron scattering angles ranged from 10\ifmmode^\circ\else\textdegree\fi{} to 133\ifmmode^\circ\else\textdegree\fi{}; the results at scattering angles larger than 20\ifmmode^\circ\else\textdegree\fi{} cannot be explained by currently available theories.