Short range interaction of nucleons inside the nucleus via He4(e,ep)R reactions

Cross sections for the He4(e,ep)R reaction have been measured for recoil momenta between 225 and 500 MeV/c. We find (1) that in the continuum channel a peak in the missing energy spectrum appears which shifts with increasing recoil momentum in a predictable way, and (2) that for the highest recoil momenta (above 300 or 350 MeV/c) overall agreement is obtained with microscopic calculations in which the scattering on nucleon pairs predominates. These results strongly suggest that the highest recoil momenta are generated by the scattering on one of a pair of nucleons. This interpretation is reinforced by an observed continuum momentum distribution which, for high recoil momenta, resembles the momentum distribution of deuterium. We infer that the high momentum part of the momentum distributioon of a nucleon pair appears unmodified when embedded in a nuclear medium.