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Manuscript Title: QCDINS 2.0 - A Monte Carlo generator for instanton-induced processes in deep-inelastic scattering.
Authors: A. Ringwald, F. Schrempp
Program title: QCDINS 2.0
Catalogue identifier: ADMI_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 132(2000)267
Programming language: Fortran.
Computer: HP 9000/735 (99 MHz).
Operating system: Linux 2.0.X, HP-UX 10.2.
RAM: 2.6M words
Keywords: QCD, Instanton, Deep-inelastic scattering, Monte Carlo simulation, Elementary particle physics.
Classification: 11.5.

Subprograms used:
Cat Id Title Reference
ACBY_v1_0 HERWIG CPC 67(1992)465
ACTU_v1_0 PYTHIA 5.7 AND JETSET 7.4 CPC 82(1994)74

Nature of problem:
Instantons are a basic aspect of Quantum Chromodynamics. Being non-perturbative fluctuations of the gauge fields, they induce hard processes absent in conventional perturbation theory. Deep-inelastic lepton-nucleon scattering at HERA offers a unique possible discovery window for such processes induced by QCD-instantons through their characteristic final-state signature and a sizable rate, calculable within instanton-perturbation theory. An experimental discovery of such a novel, non-perturbative mainifestation of non-abelian gauge theories would be of fundamental significance. However, instanton-induced events are expected to make up only a small fraction of all deep-inelastic events. Therefore, a detailed knowledge of the resulting hadronic final state, along with a multi-observable analysis of experimental data by means of Monte Carlo techniques, is necessary.

Solution method:
The QCDINS package is degigned as an "add-on" hard process generator interfaced to the general hadronic event simulation package HERWIG. It incorporates the theoretically predicted production rate for instanton-induced events as well as the essential characteristics that have been derived theoretically for the partonic final state of instanton-induced processes: notably, the flavour democratic and isotropic production of the partonic final state, energy weight factors different for gluons and quarks, and a high average multiplicity O(10) of produced partons with a Poisson distribution of the gluon multiplicity. While the subsequent perturbative evolution of the generated partons is always handled by the HERWIG package, the final hadronization step may optionally be performed also by means of the general hadronic event simulation package JETSET.

Restrictions:
The default values of the implemented kinematical cuts represent the state of the art limits for the reliability of the generated instanton-induced event rate and event topology.

Unusual features:
The program needs HERWIG version 5.9. The CPC Library version is 5.1 [1]. The HERWIG library may be downloaded from the homepage http://hepwww.rl.ac.uk/theory/seymour/herwig/.

Running time:
10 - 100 events per second for a PC with Pentium CPU, depending on its clock frequency. On a HP 9000/735 (99 MHz) workstation, 6 events per second are generated.

References:
[1] G. Marchesini et al., Comput. Phys. Commun. 67 (1992) 465.