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Manuscript Title: An efficient partial-wave analyser for the absorption model.
Authors: P.A. Collins, B.J. Hartley, R.W. Moore, K.J.M. Moriarty
Program title: EPWAAM
Catalogue identifier: AAUF_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 5(1973)349
Programming language: Fortran.
Computer: CDC 6600.
Operating system: SCOPE.
RAM: 37K words
Word size: 60
Keywords: Elementary, Particle physics, Absorption model, S-channel helicity Amplitudes, Partial-wave expansion, Rotation functions, Elastic scattering, Differential Cross section, Spin density matrix, Gaussian quadrature, X**2 minimization, Phenomenological model.
Classification: 11.6.

Nature of problem:
This program is concerned with the phenomenological analysis of high- energy 2-body scattering processes in terms of the absorption model.

Solution method:
Rather than employ the impact-parameter representation and the subsequent approximations required by such a procedure, the program expands the s-channel helicity amplitudes in exact partial-wave series, modifies the partial-wave amplitudes according to the absorption model prescription and resums the series to obtain the modified amplitudes. These amplitudes may then be compared with experiment by means of differential cross sections, polarizations, spin density matrix elements, etc. The integration to obtain the partial-wave amplitudes is performed by gaussian quadrature. By adding the minimization program MINUITS data-fitting may be performed.

Restrictions:
The number of partial-wave amplitudes which must be explicity calculated increases with the momentum of the beam particles. The program is dimensioned for 30 partial-wave amplitudes. This has been found to be quite adequate for beam momenta up to 360GeV/c.

Running time:
This depends on the number of helicity amplitudes to be calculated and on their complexity. A recent application of this program to calculate a wide range of meson-baryon scattering processes by Adjei et al. involving about 70 partial-wave expansions took approximately 120 s. When used for minimization the running time will depend on the number of parameters to be determined and on how accurately they are required.