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

Abstract

A study of the total cross section for polarized proton knockout in (e, e ′ p) reactions is carried out for the closed-shell nucleus 40 Ca. The dependence of FSI effects on polarization observables viewed as functions of the nucleon polarization angles is analyzed and interpreted within the basis of a semi-classical model for the orbit of the struck nucleon and trajectory of the ejected nucleon. A comparison with the case of a 39 K polarized target and unpolarized protons is performed.

Semirelativistic description of quasielastic neutrino reactions and superscaling in a continuum shell model

“…Moreover, the resulting semirelativistic (SR) current is simple enough to be easily implemented in already existing nonrelativistic models of (ν l , l − ) and (ν l , l + ) reactions, where l = e or µ. It is presented here as an extension of the electromagnetic and weak-neutral current expansion originally derived in [26] and that in recent years has been widely tested and applied in several Collaborations to describe a wide variety of inclusive and exclusive electron scattering observables for intermediate energies and excitations in the vicinity of the QE peak [27][28][29][30][31][32][33][34][35][36][37]. Extensions of the SR expansion to meson-exchange currents have also been developed [38,39], and a detailed description of their application to two-body currents can be found in a recent review article [40].…”

Skewed recoil polarization in (e,e′p) reactions from polarized nuclei

“…It can be shown that in the independent particle model, this is a unit vector, |v| = 1, and that, semi-classically, it coincides with the local spin field in momentum space [31,32,39] (see an example in Appendix C for the particular case of the 39 K nucleus analyzed in the next section). Since the dependence of the cross-section on the final spin direction, S l N , is linear, one can write the ith component (i = x, y, z) of the vector cross-section in the general form…”

“…500 MeV/c) the polarization induced by FSI is expected to be small (60.2). This is indicated both by experimental data [11] and by calculations [19,39]. the axes (z, x, y) used to characterize the bound nucleon (target) polarization.…”

“…In fact, for unpolarized nuclei, there are two such mechanisms: (i) For unpolarized electrons induced polarization is produced on the recoil protons by effect of the FSI with the residual nucleus. In DWIA models [39] this effect is partially due to the imaginary part of the central optical potential-which produces different absorptions for protons exiting from regions of the nucleus with different local spin directions-and partially due to the spin-orbit potential, which produces a spin-dependent interaction.…”

“…In some cases of interest, a semi-classical interpretation of the reaction mechanism producing such polarization transfer can be drawn. In fact, in the case of knock-out from the outer shell, the initial proton is carrying part of the nuclear polarization, so an expected value of the initial spin can be defined for the proton [32,39]. In general, the final direction of the recoil polarization does not coincide with the initial one, so the interaction is producing a change of the proton spin.…”