Herwig++ 1.0: An Event Generator for e+e- Annihilation
Stefan Gieseke, Alberto Ribon, Michael H Seymour, Philip Stephens, Bryan Webber
TL;DR
Herwig++ introduces a full event generator for $e^+e^-$ annihilation with a novel massive-quark aware parton shower and an improved cluster hadronization model, validated against LEP/SLC data. The framework hinges on new evolution variables $(\tilde{q}, z)$ with angular ordering and a $Q_g$ cutoff, supplemented by hard and soft matrix-element corrections and a momentum-reshuffling scheme to preserve energy. Across a broad set of observables—event shapes, jet rates, identified hadrons, and $B$ fragmentation—the approach shows improved agreement relative to previous HERWIG implementations, indicating a robust baseline for future initial-state radiation and underlying-event extensions. The work delivers a complete, tunable e+e- generator with a recommended parameter set and outlines plans to extend to hadron-hadron collisions for Tevatron/LHC-scale physics.
Abstract
Results from the new Monte Carlo event generator Herwig++ are presented. This first version simulates Hadron Emission Reactions With Interfering Gluons in electron-positron annihilation. The parton shower evolution is carried out using new evolution variables suited to describing radiation from heavy quarks as well as light partons. The partonic final state is fragmented into hadrons by means of an improved cluster hadronization model. The results are compared with a wide variety of data from LEP and SLC.