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Manuscript Title: PIPIT: a momentum space optical potential code for pions. See erratum Comp. Phys. Commun. 13(1977)141.
Authors: R.A. Eisenstein, F. Tabakin
Program title: PIPIT
Catalogue identifier: ABIH_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 12(1976)237
Programming language: Fortran.
Computer: UNIVAC 1108.
Operating system: UNIVAC EXEC II.
RAM: 35K words
Word size: 36
Keywords: Nuclear physics, Medium energy, Elastic scattering, Angular distribution, Cross section, Optical potential, Momentum space, Lippmann-schwinger, Pion.
Classification: 17.14.

Nature of problem:
Angular distributions for the elastic scattering of pions are generated by summing a partial wave series. The elastic T-matrix elements for each partial wave are obtained by solving a relativistic Lippmann- Schwinger equation in momentum space using a matrix inversion technique. The Coulomb interaction is included essentially exactly using the method of Vincent and Phatak. The piN amplitude is obtained from phase shift information on-shell and incorporates a separable off-shell form factor to ensure a physically reasonable off-shell extrapolation. The piN interaction is of finite range and a kinematic transformation procedure is used to express the piN amplitude in the pi nucleus frame.

A maximum of 30 partial waves can be used in the present version of the program to calculate the cross section. The Lippman-Schwinger equation is presently solved for each partial wave by inverting a 34 X 34 supermatrix. At very high energies, larger dimensions may be required. The present version of the code uses a separable non-local phi N potential of finite range; other types of non-localities, or non- separable potentials, may be of physical interest.

Running time:
This depends on the number of partial waves and the size of the supermatrix. The test case requires 60 sec on the UNIVAC 1108 (10 partial waves, 34 X 34 supermatrix).