Matching NLO QCD and parton showers in heavy flavour production
S. Frixione, P. Nason, B. R. Webber
TL;DR
MC@NLO is applied to heavy flavour hadroproduction to provide NLO-accurate cross sections and distributions while retaining fully exclusive hadron-level events via a consistent parton shower interface. The paper details the MC@NLO formalism, the construction of MC subtraction terms including final-state emissions and colour-flow effects, and a practical recipe to combine NLO calculations with the HERWIG shower. It discusses heavy-quark production channels, the challenges posed by flavour creation, excitation, and gluon splitting, and the limitations of MC@NLO in capturing all FEX and GSP contributions. Illustrative predictions for top and bottom production at the Tevatron and LHC are presented, highlighting improvements in realism for heavy flavour backgrounds in collider analyses.
Abstract
We apply the MC@NLO approach to the process of heavy flavour hadroproduction. MC@NLO is a method for matching next-to-leading order (NLO) QCD calculations and parton shower Monte Carlo (MC) simulations, with the following features: fully exclusive events are generated, with hadronisation according to the MC model; total rates are accurate to NLO; NLO results for distributions are recovered upon expansion in $\as$; hard emissions are treated as in NLO computations while soft/collinear emissions are handled by the MC simulation, with the same logarithmic accuracy as the MC; matching between the hard and soft regions is smooth, and no intermediate integration steps are necessary. The method was applied previously to the hadroproduction of gauge boson pairs, which at NLO involves only initial-state QCD radiation and a unique colour structure. In heavy flavour production, it is necessary to include contributions from final-state QCD radiation and different colour flows. We present illustrative results on top and bottom production at the Tevatron and LHC.