We compare different procedures for combining fixed-order tree-level matrix-element generators with parton showers. We use the case of W-production at the Tevatron and the LHC to compare different implementations of the so-called CKKW and MLM schemes
using different matrix-element generators and different parton cascades. We find that although similar results are obtained in all cases, there are important differences.
We propose to combine and slightly extend two existing Les Houches Accords to provide a simple generic interface between beyond-the-standard-model parton-level and event-level generators. All relevant information - particle content, quantum numbers o
f new states, masses, cross sections, parton-level events, etc - is collected in one single file, which adheres to the Les Houches Event File (LHEF) standard.
