Semi-relativistic meson exchange currents in (e,e') and (e,e'p) reactions

Amaro, J. E.; Barbaro, M. B.; Caballero, J. A.; Tabatabaei, F. Kazemi

Semi-relativistic meson exchange currents in (e,e') and (e,e'p) reactions

Authors

Amaro, J. E.

Barbaro, M. B.

Caballero, J. A.

Tabatabaei, F. Kazemi

Description

Electron-induced one-nucleon knock-out observables are computed for moderate to high momentum transfer making use of semi-relativistic expressions for the one-body and two-body meson-exchange current matrix elements. Emphasis is placed on the semi-relativistic form of the $Δ$-isobar exchange current and several prescriptions for the dynamical-equivalent form of the $Δ$-propagator are analyzed. To this end, the inclusive transverse response function, evaluated within the context of the semi-relativistic approach and using different prescriptions for the $Δ$-propagator, is compared with the fully relativistic calculation performed within the scheme of the relativistic Fermi gas model. It is found that the best approximation corresponds to using the traditional static $Δ$-propagator. These semi-relativistic approaches, which contain important aspects of relativity, are implemented in a distorted wave analysis of quasielastic $(e,e'p)$ reactions. Final state interactions are incorporated through a phenomenological optical potential model and relativistic kinematics is assumed when calculating the energy of the ejected nucleon. The results indicate that meson exchange currents may modify substantially the $TL$ asymmetry for high missing momentum.
24 pages, 9 figures. New version with MEC results including strong form factors. Typo errors in equations corrected. To be published in Phys. Rev. C