Agreement at last: an experimental and theoretical study on the single ionization of helium by fast proton impact

Even though ion/atom-collision is a mature field of atomic physics, great discrepancies between experiment and theoretical calculations are still common. Experimental results with highest momentum resolution on single ionization of helium induced by 1 MeV protons are presented and compared to different theoretical calculations. The overall agreement is strikingly good and already the first Born approximation yields good agreement between theory and experiment. This has been expected since several decades, but so far has not been accomplished. As previous experiments believe in the observation of projectile coherence effects on the measured data, a short review of an ongoing dispute with the existence of nodal structures in the electron angular emission distributions is given.