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Manuscript Title: POMWIG: HERWIG for diffractive interactions.
Authors: B. Cox, J. Forshaw
Program title: POMWIG 1.1
Catalogue identifier: ADPP_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 144(2002)104
Programming language: Fortran.
Operating system: Red Hat, SUSE Linux.
RAM: 9M words
Keywords: Diffraction, Monte Carlo simulation, Pomeron, Elementary particle physics, Event simulation.
Classification: 11.2.

Subprograms used:
Cat Id Title Reference
ACBY_v1_0 HERWIG 5.1 CPC 67(1992)465

Nature of problem:
The nature of the pomeron, a strongly interacting colorless exchange, has been studied widely in both proton-proton and electron-proton collisions. Factorizable models, in which the proton 'emits' a pomeron which undergoes a hard interaction with the other beam particle, have met with considerable success in electron-proton collisions [2], although their applicability in proton-proton collisions is as yet uncertain. In understanding the nature of diffraction experimentally, it is crucial to have a full simulation not only of the underlying dynamics, but also of the hadronic final state. A full Monte Carlo generator is therefore necessary to understand both the experimental data and to test factorizable models in detail.

Solution method:
POMWIG implements the factorizable pomeron model into the HERWIG Monte Carlo generator [1]. This allows diffractive collisions to be generated using all hard sub-processes available in HERWIG, with a range of beam particles, and for a full simulation of the hadronic final state. Subleading (reggeon) exchanges are also implemented. The structure of the exchange and the nature of the flux factors are user definable.
The routines supplied will function with all currently available versions of HERWIG [1] from 5.9 onwards.

The factorizable model of diffraction is fully implemented. POMWIG allows the user to implement arbitrarily complex structure functions and flux factors.

Unusual features:

Running time:
Dependent on the hard subprocess and center of mass energy of the incoming particles, but similar to HERWIG.

[1] G. Marchesini et al., Comp. Phys. Comm. 67 (1992) 465; G. Corcella et al., JHEP 0101 (2001) 010 (http://hepwww.rl.ac.uk/theory/seymour/herwig/)
[2] H1 Collaboration: C. Adloff et al., Z.Phys. C74 (1997) 221.