We describe a Monte Carlo event generator for the simulation of QCD-instanton induced processes in deep-inelastic scattering (HERA). The QCDINS package is designed 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. Keywords: QCD; Instanton; Deep-inelastic scattering; Monte Carlo simulation
Nature of physical problemInstantons 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, nonperturbative manifestation 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.
Method of solutionThe QCDINS package is designed 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 2 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 on the complexity of the problemThe 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 top...