HERWIG 6: an event generator for hadron emission reactions with interfering gluons (including supersymmetric processes)

HERWIG is a general-purpose Monte Carlo event generator, which includes the simulation of hard lepton-lepton, lepton-hadron and hadron-hadron scatteri ng and soft hadron-hadron collisions in one package. It uses the parton-sho wer approach for initial- and final-state QCD radiation, including colour c oherence effects and azimuthal correlations both within and between jets. T his article updates the description of HERWIG published in 1992, emphasisin g the new features incorporated since then. These include, in particular, t he matching of first-order matrix elements with parton showers, a more corr ect treatment of heavy quark decays, and a wide range of new processes, inc luding many predicted by the Minimal Supersymmetric Standard Model, with th e option of R-parity violation. At the same time we offer a brief review of the physics underlying HERWIG, together with details of the input and cont rol parameters and the output data, to provide a self-contained guide for p rospective users of the program.