QCD matrix elements + parton showers.

Abstract

We propose a method for combining QCD matrix elements and parton showers in Monte Carlo simulations of hadronic final states in e+e− annihilation. The matrix element and parton shower domains are separated at some value yini of the jet resolution, defined according to the kT -clustering algorithm. The matrix elements are modified by Sudakov form factors and the parton showers are subjected to a veto procedure to cancel dependence on yini to next-to-leading logarithmic accuracy. The method provides a leading-order description of hard multi-jet configurations together with jet fragmentation, while avoiding the most serious problems of double counting. We present first results of an approximate implementation using the event generator APACIC++.