Electron helicity-dependence in (e,e'p) reactions with polarized nuclei and the fifth response function

The cross section for electron-induced proton knockout reactions with polarized beam and target is computed in a DWIA model. The analysis is focused on the electron helicity-dependent (HD) piece of the cross section. For the case of in-plane emission a new symmetry is found in the HD cross section, which takes opposite values for specific opposing pairs of nuclear orientations, explaining why the fifth response (involving polarized electrons, but unpolarized nuclei) is zero for this choice of kinematics. Even when this symmetry breaks down in the case of nucleon emission out of the scattering plane, it is shown that it is still present in the separate response functions. A physical explanation of these results is presented using a semi-classical model of the reaction based on the PWIA and on the concept of a nucleon orbit with its implied expectation values of position and spin.Comment: 38 pages, 15 PS figure

Superscaling in electron- and neutrino-nucleus scattering

The superscaling properties of electron scattering data are used to extract model-independent predictions for neutrino-nucleus cross sections.Comment: Contibution to NuInt05, 4th international workshop on neutrino-nucleus interaction in the few GeV region, Sept. 26 - 29 2005, Okayama, Japa

Final-State Interactions in (e,e'p) Reactions with Polarized Nuclei

The cross section for coincidence, quasielastic proton knock-out by electrons from a polarized K39 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.Comment: 26 pages, 8 Postscript figures, uses epsf.st

Meson-exchange currents and quasielastic neutrino cross sections in the SuperScaling Approximation model

We evaluate the quasielastic double differential neutrino cross sections obtained in a phenomenological model based on the superscaling behavior of electron scattering data. We compare our results with the recent experimental data for neutrinos of MiniBooNE and estimate the contribution of the vector meson-exchange currents in the 2p-2h sector.Comment: 6 pages, 4 figure

Spin Observables in Coincidence Electron Scattering from Nuclei I: Reduced Response Functions

A theoretical description of nucleon knockout reactions initiated by polarized electron scattering from polarized nuclei is presented. Explicit expressions for the complete set of reduced response functions (independent of the polarization angle) that can be experimentally obtained assuming plane waves for the electron are given in a general multipole expansion. The formalism is applied to the particular case of closed-shell-minus-one nuclei using two models for the ejected nucleon, including the final-state interaction phenomenologically with a complex optical potential and in the factorized plane-wave impulse approximation. Relativistic effects in the kinematics and in the electromagnetic current are incorporated throughout --- specifically a new expansion of the electromagnetic current in powers only of the struck nucleon momentum is employed. Results are presented for the nucleus 39K.Comment: 51 pages (LaTeX), 17 figures (postScript

Relativistic Effects in Electromagnetic Meson-Exchange Currents for One-Particle Emission Reactions

Following recent studies of non-relativistic reductions of the single-nucleon electromagnetic current operator, here we extend the treatment to include meson exchange current operators. We focus on one-particle emission electronuclear reactions. In contrast to the traditional scheme where approximations are made for the transferred momentum, transferred energy and momenta of the initial-state struck nucleons, we treat the problem exactly for the transferred energy and momentum, thus obtaining new current operators which retain important aspects of relativity not taken into account in the traditional non-relativistic reductions. We calculate the matrix elements of our current operators between the Fermi sphere and a particle-hole state for several choices of kinematics. We present a comparison between our results using approximate current operators and those obtained using the fully-relativistic operators, as well as with results obtained using the traditional non-relativistic current operators.Comment: LaTeX, 31 pages, 7 Postscript figures, to be published in Nucl. Phys.

Inclusive quasielastic scattering of polarized electrons from polarized nuclei

The inclusive quasielastic response functions that appear in the scattering of polarized electrons from polarized nuclei are computed and analyzed for several closed-shell-minus-one nuclei with special attention paid to 39K. Results are presented using two models for the ejected nucleon --- when described by a distorted wave in the continuum shell model or by a plane wave in PWIA with on- and off-shell nucleons. Relativistic effects in kinematics and in the electromagnetic current have been incorporated throughout. Specifically, the recently obtained expansion of the electromagnetic current in powers only of the struck nucleon's momentum is employed for the on-shell current and the effects of the first-order terms (spin-orbit and convection) are compared with the zeroth-order (charge and magnetization) contributions. The use of polarized inclusive quasielastic electron scattering as a tool for determining near-valence nucleon momentum distributions is discussed.Comment: 51 LaTeX pages, 14 Postscript figure

Delta-isobar relativistic meson exchange currents in quasielastic electron scattering

We study the role of the $\Delta$-isobar current on the response functions for high energy inclusive quasielastic electron scattering from nuclei. We consider a general Lagrangian which is compatible with contact invariance and perform a fully relativistic calculation in first-order perturbation theory for one-particle emission. The dependence of the responses upon off-shell parametrizations is analyzed and found to be mild. A discussion of scaling behaviour and a comparison with various non-relativistic approaches are also presented.Comment: 26 pages, 9 figures; one page of text added; corrected errors in eq

Superscaling and Charge-changing Neutrino Cross Sections

The superscaling function extracted from inclusive electron scattering data is used to predict high energy charge-changing neutrino cross sections in the quasi-elastic and $\Delta$ regions.Comment: 3 pages, 2 figures, to appear in the Proceedings of the 7th International Workshop on Neutrino Factories and Superbeams, Laboratori Nazionali di Frascati, Frascati (Rome), June 21 - 26, 200

Scaling and isospin effects in quasielastic lepton-nucleus scattering in the Relativistic Mean Field Approach

The role of isospin in quasielastic electron scattering and charge-changing neutrino reactions is investigated in the relativistic impulse approximation. We analyze proton and neutron scaling functions making use of various theoretical descriptions for the final-state interactions, focusing on the effects introduced by the presence of strong scalar and vector terms in the relativistic mean field approach. An explanation for the differences observed in the scaling functions evaluated from $(e,e')$ and $(\nu,\mu)$ reactions is provided by invoking the differences in isoscalar and isovector contributions.Comment: 10 pages, 5 figures, submitted to Phys. Lett.