Final-state interactions in (e, e′p) reactions with polarized nuclei

Abstract

The cross section for coincidence, quasielastic proton knock-out by electrons from a polarized 39 K nucleus is computed in DWIA using an optical potential in describing the wave function of the ejected nucleon. The dependence of the FSI on the initial polarization angles of the nucleus is analyzed and explained in a new, semi-classical picture of the reaction in which the nuclear transparency decreases as a function of the amount of nuclear matter that the proton has to cross, thus providing a method for obtaining detailed information on its mean free path in finite nuclei. We propose a procedure to find the best initial kinematical conditions for minimizing the FSI which will be useful as a guide for future experiments with polarized nuclei.

Final-state interaction and recoil polarization in reactions: comparison with the polarized target case

“…In these reactions the dominance of one side of the nucleus (with respect to the final momentum of the nucleon, p ′ ) emphasizes a definite orientation of the initial orbit, and then also favors a definite orientation of the nucleon spin. An analogous effect was independently predicted for (e, e ′ p) reactions from polarized nuclei in [25]. Therein the effects of FSI on the cross section were shown to depend strongly on the nuclear orientation.…”

“…The results found in [25] and later extended to polarized electrons in [26] provide a clear geometric picture of these reactions on polarized nuclei. One of the aims of the present paper is to investigate the degree to which this picture can be extended to the case of induced nucleon polarization in (e, e ′ p) reactions with unpolarized targets.…”

“…Second we use the so-called semi-relativistic form of the nuclear (one-body) electromagnetic current operator, J µ (q), obtained as an expansion in powers of p/m N , the missing momentum over the nucleon mass, maintaining the exact dependence on the energy-momentum transfer. The resulting semi-relativistic DWIA model (SR-DWIA) was applied to (e, e ′ p) reactions from polarized nuclei in [25,26,36], to recoil polarization observables in [11,12], and to the unpolarized reaction in [35,39,41]. Effects beyond the impulse approximation due to meson-exchange currents (MEC) were discussed in [11,12,35] -it can be shown that they do not affect the results of the present work significantly.…”

“…The asymptotic nucleon state |p ′ s , with spin in the s direction, is computed in DWIA as a solution of the Schrödinger equation with an optical potential. In the particular case of the results for 40 Ca of the next section, we use the potential parameterization of Schwandt [40], the same considered in [25] since we want to compare with the results for polarized nuclei using the same interaction. The present model accounts for relativistic corrections that have proven to be successful in describing intermediate-energy inclusive and exclusive electron scattering observables in the region of the quasielastic peak [41,42,43,44,45].…”

“…Analyses of the complete set of polarization observables in (e, e ′ p) only exist for the case of light nuclei, in particular deuterium [28]- [33,34], but not for mediumweight nuclei. In the present paper we apply the DWIA model of [11,12,35] to describe proton knockout from the d 3/2 shell of 40 Ca for various recoil polarization directions, and compare the results with those found for the model of [25,26,36] of proton knockout from the same shell of polarized 39 K.…”