The implementation of the four-jet matrix elements in HERWIG and   elsewhere
  The new version 6.1 of the HERWIG event generator allows one to simulate hadronic final states in electron-positron annihilations using the $O(\alpha_s^2)$ partonic matrix elements (MEs) for $e^+e^-\to q\bar qgg$ and $e^+e^-\to q\bar q Q\bar Q$. The consequent phenomenology is discussed in the case of four-jet signatures of particular relevance to future electron-positron Linear Colliders (LCs), such as in Higgs boson searches. The new approach adopted in HERWIG is compared to the standard $O(\alpha_s)$ description, as well as to other recently presented event generators also based on $e^+e^-\to4$ parton MEs. 
S. Moretti (RAL)