Ionization cross sections for proton - helium collisons doubly differential in projectile scattering angle and electron energy

We have measured angular distributions of proton projectiles suffering specific energy loss in collisions with helium target atoms. From this data, we obtained cross sections for single ionization doubly differential in projectile scattering angle and ionized electron energy. Angular distributions were taken at an incident energy of 100 keV and energy loss values ranging from 35 to 150 eV. Preliminary results are also shown for 175 keV incident energy. This data will be discussed in context with structures in singly differential cross sections recently observed experimentally, and found in theoretical calculations