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Manuscript Title: Calculation of the virtual photon spectrum in distorted wave analysis.
Authors: L.E. Wright, C.W. Soto Vargas
Program title: VIRT SPEC
Catalogue identifier: ABPJ_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 20(1980)337
Programming language: Fortran.
Computer: IBM 370/158.
Operating system: VS1.
RAM: 27K words
Word size: 32
Keywords: Elementary, Particle physics, Quantum electrodynamics, Virtual photon spectrum, Distorted wave, Electron scattering, Dirac-coulomb.
Classification: 11.4.

Nature of problem:
The virtual photon spectrum accompanying electrons or positrons scattering from a point charge Z is calculated in plane wave Born approximation and in distorted wave Born approximation for E1, E2, E3 and M1 multipoles.

Solution method:
The radial integrals over Dirac-Coulomb functions and the spherical Hankel function are evaluated analytically. The summation over partial waves is carried out by using the fact that matrix elements involving higher partial waves have very little Coulomb distortion effects and can be replaced by plane wave matrix elements which can be summed analytically.

Restrictions:
The present code is only valid in the point nucleus limit. Thus, the interpretation of experiments with lepton momenta such that there is appreciable nuclear penetration in terms of virtual photon spectra is open to question. Also, the present code was programmed assuming relativistic leptons, Ei >10 ; and is not suitable for low energy muons except for photon energies well away from the end point. The restrictions on the allowed multipoles, E1,E2,E3 and M1 are only made for convenience, and can be relaxed by including additional analytic expressions in the subroutine PWAVE. Also, for storage purposes, only 30 different photon energies can be calculated with one set of data cards using the energy propagation. Of course, additional data cards can be used to propagate and calculate another 30 values.