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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.

Restrictions:
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.

References:
[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.