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Manuscript Title: Hard diffractive scattering in high energy ep collisions and the Monte Carlo generator RAPGAP.
Authors: H. Jung
Program title: RAPGAP version 1.0
Catalogue identifier: ADAR_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 86(1995)147
Programming language: Fortran.
Computer: IBM.
Operating system: MVS.
Keywords: Particle physics, Elementary, Event simulation, Perturbative quantum Chromodynamics (qcd), Diffractive ep Scattering, Hard scattering, Pomeron, Cross sections.
Classification: 11.2.

Nature of problem:
Inelastic ep scattering is an ideal tool to study properties of a possible partonic (quark or gluon) nature of the pomeron. Partonic interactions of the photon with quarks and gluon coming from the pomeron are calculated. Such kind of events have a gap in energyflow between the fast moving proton and the rest of the hadronic system. Such events have been found recently in the experiments at the HERA collider [1,2].

Solution method:
A new Monte Carlo program has been written including the following partonic subprocesses: gammag -> qqbar gammag -> ccbar eg -> e'qqbar eg -> e'ccbar eq -> e'q' The program can be used for deep inelastic scattering as well as for photoproduction. QCD parton showers are included with the color-dipole-model (ARIADNE) [3]. The subsequent fragmentation is done with JETSET 7.3 [4]. Several options for the parametrization of the pomeron flux are available as well as different choices for the density of partons in the pomeron.

At present all subprocesses have to be generated separately. For photo- production only the direct photon interactions are implemented.

Unusual features:
not known

Running time:
Generation of a complete event takes approximately 0.13 s on SGI.

[1] M. Derrick et al., ZEUS Collaboration, DESY preprint 93-093 (1993) and Phys. Lett. B315, 481 (1993)
[2] T. Ahmed et al., H1 Collaboration, DESY preprint to be published (1994).
[3] L. Lonnblad, DESY preprint 92-046 and Comp. Phys. Commun. 71(1992)15.
[4] T. Sjostrand, PYTHIA 5.6 and JETSET 7.3, CERN-TH-6488/92 T. Sjostrand, Comp. Phys. Commun. 39(1986)347, ibid.