Merging meets matching in MC@NLO

Abstract

Abstract:The next-to-leading order accuracy for MC@NLO results exclusive in J light jets is achieved if the computation is based on matrix elements that feature J and J +1 QCD partons. The simultaneous prediction of observables which are exclusive in different light-jet multiplicities cannot simply be obtained by summing the above results over the relevant range in J; rather, a suitable merging procedure must be defined. We address the problem of such a merging, and propose a solution that can be easily incorporated into existing MC@NLO implementations. We use the automated aMC@NLO framework to illustrate how the method works in practice, by considering the production at the 8 TeV LHC of a Standard Model Higgs in association with up to J = 2 jets, and of an e + ν e pair or a tt pair in association with up to J = 1 jet.

Drell-Yan production atNNLL′+NNLOmatched to parton showers

“…(22) in the longitudinally boosted frame where the vector boson has zero rapidity. The reference vectors for the beam directions are always along the beam directions, soñ a ¼ẑ andñ b ¼ −ẑ.…”

“…[8][9][10][11][12][13][14][15][16][17][18]. By now there are several methods available to combine multiple NLO calculations with parton showers [19][20][21][22][23][24][25][26][27]. More recently, combinations of specific Drell-Yan-like next-to-next-to-leading order (NNLO) calculations with parton showers have been presented in Refs.…”

Measurement of the forward Z boson production cross-section in pp collisions at s = 13 $$ \sqrt{s}=13 $$ TeV

“…Different schemes are used to match and merge these samples. The MLM [30] sample has leading-order accuracy for the emission of zero, one or two jets; the FxFx [31] sample has next-to-leading-order (NLO) accuracy for zero-or one-jet emission; and the UNLOPS [32] sample is accurate at NLO for zero-or one-jet emission and accurate at LO for two-jet emission. Higher jet multiplicities are generated by a parton shower, implemented here using the Monash 2013 tune for Pythia 8.…”

Soft evolution of multi-jet final states

“…They can be merged with LO predictions for multi-jet events [31][32][33][34] and matched to NLO calculations [35][36][37] for over a decade. More recently, methods for combining next-to-leading order matched predictions of varying jet multiplicity have been devised [38][39][40], as well as matching methods at next-to-next-to leading order (NNLO) accuracy [41][42][43]. Dedicated Monte Carlo programs aimed at better describing jet production in the high-energy limit have also been developed [44].…”