The 2-Body Electrodisintegration Of He-4 Studied Through The (E, E''p) Reaction

Coincidence cross sections obtained with the (e, e''p) reaction are presented for the He-4 nucleus. From the measurements, performed in non-parallel kinematics at a relative p-H-3 kinetic energy in the center-of-mass system of 75 MeV, the proton-triton momentum distribution for recoil momenta up to 350 MeV/c has been extracted. The results show a strong dependence on the kinematical configuration. In order to study this in more detail we extended the He-4(e, e''p)H-3 experiments to other kinematics, both parallel and non-parallel, and compare these data to phenomenological and microscopic calculations. The phenomenological treatment consists of a distorted-wave impulse approximation (DWIA) analysis using an optical potential. Charge-exchange effects in the final state are accounted for through coupled-channels calculations using the Lane formalism. These phenomenological calculations do not agree with the data. The microscopic calculation, which employs a diagrammatic treatment including the charge-exchange process (e, e''n)(n, p), proton rescattering effects and the contributions from meson-exchange currents, accounts fairly well for the empirical observations. The momentum dependence of the data is compared with theoretical calculations obtained with the VMC and ATMS variational methods for the Urbana and RSC nucleon-nucleon potentials. The results for the Urbana V14 NN potential, including corrections to PWIA using the microscopic model, are in good agreement with the data. The (e, e''n)(n, p) two-step contribution turns out to be an important ingredient for obtaining a satisfactory description of the He-4(e, e''p)H-3 cross sections. Sum-rule results are presented and the data are compared to results of (p, 2p) and other (e, e''p) experiments.