NLO accuracy in modern Monte-Carlo event generators, Frank Siegert (Uni Freiburg)

Different approaches to achieve QCD NLO accuracy in full hadron-level Monte Carlo event generators are reviewed. Due to the double counting between real emission parts in a NLO calculation and parton shower emissions on top of Born-like events a matching prescription (NLO+PS) has to be implemented. Schemes like the original MC@NLO method, and POWHEG as a variant of it, are introduced. More recently, it has become possible to merge multiple such NLO+PS samples for different jet multiplicities, to achieve NLO accuracy in different jet multiplicities simultaneously without double counting. Examples of the improvements achieved with these methods are given, with a focus on the agreement with experimental data and reduction of perturbative uncertainties.