L. E. Wright

A computer program for analysis of inelastic electron scattering from nuclei

Abstract A partial wave analysis of inelastic electron scattering is carried out for electric and magnetic multipole excitations of the nucleus. The results of this analysis which includes the effects of energy loss and Coulomb retardation have been programmed for the computer. The resulting FORTRAN IV program is capable of calculating inelastic electron scattering differential and total cross sections for a large range of incident electron energies and transitions of multipolarity 1 to 5. The methods of calculation and the limitations of the program are discussed in some detail.

Quasifree kaon photoproduction on nuclei

Abstract 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.

Virtual photons in pion electroproduction

Abstract We examine the applicability of the virtual photon spectrum to pion production experiments by using an exact calculation of pion electroproduction from the proton and from 3He. After deriving a new virtual spectrum formula which takes into account the recoil of light target nuclei and the proper electron kinematics near the endpoint, we find that the concept of a virtual photon spectrum in such experiments is very good.

Final-state Lambda-neutron interaction in kaon photoproduction from the deuteron

The effects of the Lambda n interaction on cross sections and Lambda polarization in the reaction ( gamma +d to K++ Lambda 0+n) are investigated in the spirit of the impulse approximation for three different potential models which have quite different scattering lengths and effective ranges. The authors find the interaction causes a significant enhancement of the cross section for the exclusive process d( gamma , K+ Lambda 0)n for selected kinematics near threshold, and not so significant an enhancement for the inclusive process d( gamma , K+) Lambda 0n. The produced Lambda tends to be depolarized and the polarization is sensitive to the potentials considered. The authors suggest that this reaction be used to extract information on the Lambda-neutron interaction by experiments being proposed for the new accelerators.

Longitudinal response functions for 40Ca from quasi-elastic electron scattering

Abstract Longitudinal response functions were extracted from quasi-elastic electron scattering data on 40 Ca at angles of 45.5°, 90°, and 140° with bombarding energies ranging from 130 to 840 MeV and for constant three-momentum transfers of 300, 330, 370, 410 and 450 MeV/ c . Contrary to previously reported results, the present longitudinal response functions show no more than 20% missing strength when compared to the relativistic Fermi gas model. Calculations employing wavefunctions generated from a relativistic Hartree potential and using an effective momentum approximation yield results that are in much closer agreement with the experimental data and indicate essentially no longitudinal suppression.

A new technique for calculating virtual photon spectra

Abstract A first-order matrix differential equation in energy is used to propagate radial matrix elements arising in DWBA of relativistic electron scattering from nuclei. Given an initial set of matrix elements at some value of the energy, this equation permits the evaluation of the radial matrix elements over the complete energy transfer range. A computer code has been written for this new procedure and the virtual photon spectra accompanying electron scattering from a point nucleus is calculated as a function of photon energy for various multipoles, nuclear charges, and incident electron energies.

Approximate Coulomb distortion effects in (e,e{sup {prime}}p) reactions

In this paper we apply a well-tested approximation of electron Coulomb distortion effects to the exclusive reaction (e,e{sup {prime}}p) in the quasielastic region. We compare the approximate treatment of Coulomb distortion effects to the exact distorted wave Born approximation evaluated by means of partial wave analysis to gauge the quality of our approximate treatment. We show that the approximate Mo/ller potential has a plane-wave-like structure and hence permits the separation of the cross section into five terms which depend on bilinear products of transforms of the transition four current elements. These transforms reduce to Fourier transforms when Coulomb distortion is not present, but become modified with the inclusion of Coulomb distortion. We investigate the application of the approximate formalism to a model of {sup 208}Pb(e,e{sup {prime}}p) using Dirac-Hartree single particle wave functions for the ground state and relativistic optical model wave functions for the continuum proton. We show that it is still possible to extract, albeit with some approximation, the various structure functions from the experimentally measured data even for heavy nuclei. {copyright} {ital 1997} {ital The American Physical Society}

Relativistic effects in kaon photoproduction from 12C

Abstract Kaon photoproduction from 12 C is investigated in the framework of a relativistic impulse approximation using Dirac single-particle wave functions. Using plane waves for the kaons, the matrix elements are evaluated in momentum space. Relativistic effects, resulting mainly from the small components of the Dirac bound states, are found to be large and may be observable in future experiments.

Radial integrals with finite energy loss for Dirac–Coulomb functions

Analytic results for radial integrals over products of Dirac–Coulomb functions and the radial part of the electromagnetic Green’s function are expressed in terms of a matrix generalization of the gamma function. This matrix gamma function has many useful properties, including a recurrence relation similar to that of the gamma function, and provides a compact easily manipulated method of evaluating the Dirac–Coulomb radial integrals. These results can be used to calculate the virtual and real photon spectra associated with electron scattering from the nucleus.

Quasi-free η photoproduction from nuclei

Abstract Quasi-free η photoproduction from nuclei is studied in the Distorted-Wave Impulse Approximation (DWIA). The elementary η production operator contains Born terms, vector meson and nucleon resonance contributions and provides an excellent description of the recent low-energy Mainz measurements on the nucleon. The resonance sector includes the S 11 (1535), P 11 (1440) and D 13 (1520) states whose couplings are fixed by independent electromagnetic and hadronic data. Different models for the ηN t -matrix are used to construct a simple ηA optical potential based on a tϱ approximation. We find that the exclusive A ( γ , ηN ) B process can be used to study medium modifications of the N ∗ resonances, particularly if the photon asymmetry can be measured. The inclusive A ( γ , η ) X reaction is compared to new data obtained on 12 C, 40 Ca, and is found to provide a clear distinction between different models for the ηN t -matrix, and we find that the imaginary part of the ηN scattering length is only about 0.12 fm.