A relativistic single-particle model is used to calculate the inclusive $(e,{e}^{'})$ reaction from $A=12$, 40, 56, 197, and 208 nuclei in the quasielastic region. We have shown that this model provides a very good description of the available experimental cross sections when they are dominated by the quasielastic process. In this paper, we use this model to investigate the dependence of $y$ scaling on electron kinematics, particularly the electron scattering angle, for a range of squared four-momentum transfer of 0.20--0.80 (GeV/$c$)${}^{2}$. In this kinematic domain, Coulomb distortion of the electron does not significantly affect scaling, but final state interactions of the knocked out nucleon do affect scaling, particularly when the nucleons have lower energies. In general, we find that scaling works for this reaction, but at lower values of the four-momentum transfer, the scaling function does have some dependence on the electron scattering angle. We also consider a modification of $y$ scaling to include small binding energy effects as a function of $Z$ and $A$ and show that there is some improvement in scaling.

We develop a Lorentz- and gauge-invariant dynamical model for pion electroproduction in the resonance region. The model is based on solving the Salpeter (instantaneous) equation for the pion-nucleon interaction with a hadron-exchange potential. We find that the one-particle-exchange kernel of the Salpeter equation for pion electroproduction develops an unphysical singularity for a finite value of Q(2). We analyze two methods of dealing with this problem. Results of our model are compared with recent single-polarization data for pion electroproduction.

Using a relativistic mean-field single particle knock-out model for (e,e') reactions on nuclei, we investigate approximate treatments of Coulomb distortion effects and the extraction of longitudinal and transverse structure functions. We show that an effective momentum approximation (EMA) when coupled with a focusing factor provides a good description of the transverse contributions to the (e,e') cross sections for electron energies above 300 MeV on 208Pb. This approximation is not as good for the longitudinal contributions even for incident electron eneriges above 1 GeV and if one requires very precise extraction of longitudinal and transverse structure functions in the quasielastic region it is necessary to utilize distortion factors based on a nuclear model and a more accurate inclusion of Coulomb distortion effects.

We obtain the electromagnetic form factors of the gammaNDelta transition by analyzing recent pion-electroproduction data using a fully relativistic dynamical model. Special care is taken to satisfy Ward-Takahashi identities for the Born term in the presence of form factors, thereby allowing the use of realistic electromagnetic form factors of the nucleon and pion. We parametrize the Q(2) dependence of the bare gammaNDelta form factors by a three-parameter form which is consistent with the asymptotic behavior inferred from QCD. The parameters of the bare gammaNDelta form factors are the only free parameters of the model and are fitted to the differential cross-section and multipole-analysis data up to Q(2)=4(GeV/c)(2) in the Delta(1232)-resonance region. This analysis emphasizes the significance of the pion-cloud effects in the extraction of the resonance parameters.

Considering two-body integral equations we show how they can be dimensionally reduced by integrating exactly over the azimuthal angle of the intermediate momentum. Numerical solution of the resulting equation is feasible without employing a partial-wave expansion. We illustrate this procedure for the Bethe-Salpeter equation for pion-nucleon scattering and give explicit details for the one-nucleon-exchange term in the potential. Finally, we show how this method can be applied to pion photoproduction from the nucleon with piN rescattering being treated so as to maintain unitarity to first order in the electromagnetic coupling. The procedure for removing the azimuthal-angle dependence becomes increasingly complex as the spin of the particles involved increases.

A relativistic mean-field single particle knockout model is compared to inclusive electron scattering ${(e,e}^{\ensuremath{'}})$ from a range of nuclei ${(}^{12}\mathrm{C},$ ${}^{56}\mathrm{Fe},$ and ${}^{197}\mathrm{Au})$ at high electron energy, but in kinematics where the cross section is dominated by the quasielastic response. These experiments were done with incident electron energies of approximately 2 GeV at SLAC with four-momentum transfer squared of approximately $0.20--0.30(\mathrm{GeV}{/c)}^{2}.$ We include the effects of electron Coulomb distortion in the calculation, and propose a simple way of including Coulomb distortion at high energies which can be used to analyze newer ${(e,e}^{\ensuremath{'}})$ experiments at Jefferson Lab. The effects of the predicted weakening of the strong scalar and vector potentials of the $\ensuremath{\sigma}\ensuremath{-}\ensuremath{\omega}$ model at high nucleon kinetic energy are included in our model.

The quasielastic electron scattering contributions to the (e,e(')) and (e,e(')p) reactions for medium and heavy nuclei depend on the nucleon electric and magnetic form factors in the nucleus. We investigate experimental data for the (e,e(')) reaction taken at SLAC on C-12, Fe-56, and Au-197 at four-momentum transfers up to 0.28 (GeV/c)(2) and for the (e,e(')p) reaction at Jefferson Lab on O-16 at four-momentum transfer of 0.8 (GeV/c)(2). Using a relativistic mean field "single-particle" theoretical model that successfully describes experimental data at lower energies and momentum transfers, we find no evidence for a modification of the nucleon form factors from their free space values for the inclusive (e,e(')) reactions and suggest that the exclusive reaction (e,e(')p) with high precision data may provide an even tighter constraint on possible medium modifications of the proton form factors.

Quasielastic electron scattering $(e,e')$ from $^{56}$Fe is calculated at large electron energies (2-4 GeV) and large three momentum transfer (0.5-1.5 GeV/c). We use a relativistic mean-field single particle model for the bound and continuum nucleon wavefunctions based on the $σ-ω$ model and we include the effects of electron Coulomb distortion in the calculation. The calculations are compared to high energy data from SLAC and more recent data from Jefferson Laboratory, particularly for kinematics where the energy transfer is less than 500 to 600 MeV and the quasielastic process is expected to dominate the cross section. The effects of the predicted weakening of the strong scalar and vector potentials of the $σ-ω$ model at high energy are investigated. Possible evidence for `longitudinal suppression' or modifications of nucleon form factors in the medium is considered, but neither is necessary to explain the quasielastic data for four momentum transfers less than 1 (GeV/c)$^2$.

Investigations of the quasifree reaction A(γ,KY )B are presented in the distorted wave impulse approximation (DWIA). For this purpose, we present a revised tree-level model of elementary kaon photoproduction that incorporates hadronic form factors consistent with gauge invariance, uses SU(3) values for the Born couplings and uses resonances consistent with multi-channel analyses. The potential of exclusive quasifree kaon photoproduction on nuclei to reveal details of the hyperon-nucleus interaction is examined. Detailed predictions for the coincidence cross section, the photon asymmetry, and the hyperon polarization and their sensitivities to the ingredients of the model are obtained for all six production channels. Under selected kinematics these observables are found to be sensitive to the hyperon-nucleus final state interaction. Some polarization observables are found to be insensitive to distortion effects, making them ideal tools to search for possible medium modifications of the elementary amplitude. PACS numbers: 25.20.Lj, 13.60.Le, 13.75.Ev, 13.88.+e Typeset using REVTEX

In response to recent experimental studies we investigate Coulomb distortion effects on (e,e') reactions from medium and heavy nuclei for the case of electrons and positrons. We extend our previously reported full distorted-wave Born approximation treatment of Coulomb distortions to the case of positrons for the Pb-208 (e,e') reaction in the quasielastic region for a particular nuclear model. In addition, we use previously reported successful approaches to treating Coulomb corrections in an approximate way to calculate the Coulomb distortion effects for (e,e') reactions for both electrons and positrons for the case of a simple nuclear model for quasielastic knockout of nucleons. With these results in hand we develop a simple ad hoc approximation for use in analyzing experiments, and discuss methods of extracting the "longitudinal structure function" which enters into evaluation of the Coulomb sum rule. These techniques are generally valid for lepton induced reactions on nuclei with momentum transfers greater than approximately 300 MeV/c.

Investigations of the quasifree reaction A(γ, KY)B are presented in the distorted wave impulse approximation (DWIA). For this purpose, we present a revised tree-level model of elementary kaon photoproduction that incorporates hadronic form factors consistent with gauge invariance, uses SU(3) values for the Born couplings and uses resonances consistent with multichannel analyses. The potential of exclusive quasifree kaon photoproduction on nuclei to reveal details of the hyperon–nucleus interaction is examined. Detailed predictions for the coincidence cross section, the photon asymmetry, and the hyperon polarization and their sensitivities to the ingredients of the model are obtained for all six production channels. Under selected kinematics these observables are found to be sensitive to the hyperon–nucleus final-state interaction. Some polarization observables are found to be insensitive to distortion effects, making them ideal tools to search for possible medium modifications of the elementary amplitude.

Cross sections are presented for the ${}^{16}\mathrm{O}(\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}},{\ensuremath{\pi}}^{\ensuremath{-}}p)$ reaction at incident photon energies between 290 and 325 MeV. The data are presented for specific proton and pion angles as a function of proton energy, which are compared with calculations in a local distorted wave impulse approximation model. The results are in agreement at most kinematics, although at some kinematics the data and calculations disagree by a factor of 2 or more. These data do not support the conclusion of a large modification to the mass of the $\ensuremath{\Delta}$ resonance in the nucleus.

We review the opportunities and challenges in the field of hypernuclear physics with electromagnetic probes. An overview is presented regarding our current understanding of the elementary production process on the nucleon. This amplitude is then used in the nuclear environment to study the hyperon-nucleon (YN) interaction. We discuss two scenarios: hypernuclear excitation that allows the investigation of hypernuclear structure and the bound Lambda in the nucleus, and quasifree kaon production on the deuteron and on nuclei, which permits a more direct access to the YN force. Specific examples are given for few-body systems and shell-model nuclei.

A measurement of the C-12(gamma,pi(+)n)B-11 reaction in quasifree pi-production kinematic regimes has been performed using tagged photons in conjunction with large solid angle pi and n detectors. The aim of the experiment was to investigate predicted modifications to the Delta excitation of nucleons and their subsequent propagation and decay, brought about by the nuclear medium. Differential cross sections an presented for photon energies spanning the Delta(1232) excitation region. The measurements are consistent with distorted wave impulse approximation calculations in which the amplitude for proton Delta excitation, followed by Delta propagation and decay to pi(+)+n, is reduced compared to that for a free p. However, because of uncertainties in the magnitudes of the final state interactions, it is concluded that improved calculations are required to obtain a quantitative estimate of Delta-medium effects.