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[Licence| Download | New Version Template] abvw_v1_0.gz(53 Kbytes)
Manuscript Title: A program for fitting and plotting amplitudes, polarization and differential cross section data for two-body reactions.
Authors: R.W.B. Ardill, K.J.M. Moriarty, P. Koehler
Program title: EXCAMP
Catalogue identifier: ABVW_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 22(1981)419
Programming language: Fortran.
Computer: CDC 6600.
Operating system: NOS/BE.
RAM: 53K words
Word size: 60
Peripherals: graph plotter.
Keywords: Elementary, Particle physics, Event reconstruction, S-channel helicity Amplitudes, Amplitude analysis, Polarization, Wolfenstein parameters, Differential cross, Section, Gribov-reggeon calculus, Chi-square minimization.
Classification: 11.9.

Subprograms used:
Cat Id Title Reference
ACWH_v1_0 MINUIT CPC 10(1976)343
AAUN_v1_0 APLOT CPC 9(1975)85

Nature of problem:
This program is concerned with the phenomenological analysis of high- energy scattering processes in terms of chi-square fits to amplitude, polarization and differential cross section data. Although the program is written for a model of the amplitudes using the Gribov-Reggeon calculus it can be readily adapted by the user to all other models.

Solution method:
Amplitude analysis has become an important tool in obtaining phenomenological models for high-energy scattering. Procedures, which only fit differential cross sections, do not give enough control on all the features of the model used. The amplitudes were fitted using the scheme of Halzen and Michael where the isovector amplitudes are defined relative to the isoscalar nonflip amplitude. The program could, however, be readily adapted to produce fits to the real and imaginary parts of the amplitudes (e.g. the pion-nucleon amplitude analysis of Hohler et al. The program is designed to be used under control of the MINUITS minimization package; a considerable amount of core can be saved when no fitting is required, if MINUITS is replaced by a routine to read in the MINUITS parameters. Plotting of amplitudes, polarization and differential cross sections is achieved using APLOT and WORDS routine (together with associated routines), the latter for producing the special lettering used. Again the program is designed so that when no plotting is required (e.g. when fitting) the plotting packages can be omitted with core saved.

To save computing time, since the program was only used for phi -p -> phi**0 n with amplitude fitting only at 6 GeV/c, the phase prescription due toAmbats et al. for the isoscalar amplitude was used to produce the required parallel and perpendicular components of amplitudes. This restriction can easily be removed; the user could calculate his own isoscalar amplitudes and use them to produce the required isovector amplitude components. Certain other restrictions on the number of processes, number of energy sets, number of data sets and number of experimental points, are described in the comment section of the routine FCN; these are connected with the dimensions of arrays used and can be reset by the user.

Running time:
The test run (no minimization) took 60 s of which 17 s was compilation time. On a minimization run, when the program was operating at its most efficient rate, time taken per call to the routine FCN (for total x**2 calculation) was about 0.22 s.