Comprehensive out-of-plane ($e,2e$) measurements and calculations on He autoionizing levels

Out-of-scattering-plane $(e,2e)$ measurements and calculations are reported for the three singlet helium $2\ell2\ell'$ auto\-ionizing levels, with 80, 100, 120, 150, and 488 eV incident-electron energies, and scattering angles 60$^\circ$, 50.8$^\circ$, 45$^\circ$, 39.2$^\circ$, and 20.5$^\circ$, respectively. The kinematics are the same in all cases: the momentum transfer is $K=2.1$~a.u., and ejected electrons are detected in a plane that contains the momentum transfer direction and is perpendicular to the scattering plane. The results are presented as $(e,2e)$ angular distributions energy-integrated over each level. They are compared with fully non\-perturbative \hbox{$B$-spline} \hbox{$R$-matrix} and hybrid second-order distorted-wave + \hbox{$R$-matrix} calculations.