Report of the QCD Working Group

TL;DR

The report surveys QCD-focused efforts to understand and simulate multi-jet final states in $e^+e^-$ collisions at LEP, emphasizing four-jet topologies and $b$-quark mass effects. It documents developments and tuning of major event generators PYTHIA, HERWIG, ARIADNE, and introduces the new multi-jet generator APACIC++. The work covers inclusive jet rates across flavours, quark-mass impacts on three- and four-jet rates, and the interplay of mass, higher-order, and hadronization effects in four-jet angular and shape distributions, as well as $b$-quark fragmentation and gluon splitting into $b\bar{b}$, underscoring advances in precision QCD modelling for LEP2 analyses.

Abstract

The activities of the QCD working group concentrated on improving the understanding and Monte Carlo simulation of multi-jet final states due to hard QCD processes at LEP, i.e. quark-antiquark plus multi-gluon and/or secondary quark production, with particular emphasis on four-jet final states and b-quark mass effects. Specific topics covered are: relevant developments in the main event generators PYTHIA, HERWIG and ARIADNE; the new multi-jet generator APACIC++; description and tuning of inclusive (all-flavour) jet rates; quark mass effects in the three- and four-jet rates; mass, higher-order and hadronization effects in four-jet angular and shape distributions; b-quark fragmentation and gluon splitting into b-quarks.