Simple classification of final state interaction effects in ⁴He(e,e'p) scattering

The radius of interaction between the struck proton and spectator nucleons is close to the radius of short-distance two-nucleon correlations in nuclear matter, which makes final state interaction(FSI) an important background to production of protons with large missing momentum. We present a simple classification of the dominant FSI effects in $^4He(e,e'p)$ scattering and identify parts of the phase space dominated by FSI. At large missing momentum, FSI leads to a striking angular anisotropy of the missing momentum distribution, which has a prominent peak in transverse kinematics and smaller, forward-backward asymmetric, peaks in parallel kinematics.