to certain restrictions), in practice they are known to do much better than that, as comparisons with data and with analytically-resummed results clearly show. Furthermore, PSMCs are fully flexible, give one the possibility of including hadronization models in a consistent manner, and are the workhorses of experimental collaborations, thanks to their capabilities of simulating fully-realistic final-state configurations that can undergo detector simulations.

As is well known, the approximations that form the core of PSMCs severely limit their predictive power in those phase-space regions (corresponding to multi-jet configurations) which are of interest for most of new-physics searches at colliders. These limitations can be alleviated by viewing PSMC predictions as resummed results, to be included with the NLO corrections to the relevant production processes into a matched cross section. The definition of a formalism for matching NLO computations and MC simulations has attracted a considerable amount of attention. There are now several proposals, but only two of them, namely MC@NLO [@Frixione:2002ik] or POWHEG [@Nason:2004rx], have made it to the stage of actually implementing several hadroproduction processes, and of being routinely used by experimental collaborations.

The MC@NLO formalism requires the computation of the cross section predicted by the PSMC at ${\cal O}({\alpha_{{\scriptscriptstyle}S}}^{b+1})$. Because 