Higgs pair production at the LHC with NLO and parton-shower effects

R Frederix,S Frixione,V Hirschi,F Maltoni,O Mattelaer,P Torrielli,E Vryonidou,M Zaro

doi:10.1016/j.physletb.2014.03.026

Abstract

We present predictions for the SM-Higgs-pair production channels of relevance at the LHC: gluon–gluon fusion, VBF, and top-pair, W, Z and single-top associated production. All these results are at the NLO accuracy in QCD, and matched to parton showers by means of the MC@NLO method; hence, they are fully differential. With the exception of the gluon–gluon fusion process, for which a special treatment is needed in order to improve upon the infinite-top-mass limit, our predictions are obtained in a fully automatic way within the publicly available MadGraph5_aMC@NLO framework. We show that for all channels in general, and for gluon–gluon fusion and top-pair associated production in particular, NLO corrections reduce the theoretical uncertainties, and are needed in order to arrive at reliable predictions for total rates as well as for distributions.

Highlights

Present LHC data provide evidence that the scalar particle observed at the LHC is the one predicted by the Brout–Englert– Higgs symmetry breaking mechanism [1,2] of SU(2)L × U (1)Y as implemented in the Standard Model (SM) [2]
We limit ourselves to pointing out that H H production via gluon–gluon fusion is computed at the NLO in a “loop-improved” effective field theory (EFT) approach, using the exact one-loop real-emission and improved one-loop virtual matrix elements; that in the case of ttH H and t j H H production exact NLO QCD results are presented in this paper for the first time; and that by matching NLO computations to parton showers we generate samples of events, for the first time, for each of the production channels, which can be used for fully realistic simulations, including those at detector level
While it is possible to obtain predictions at the ME + PS level in this work we limit ourselves to NLO + PS results. This is because the smallness of the Higgs-pair cross sections rather emphasises observables which are inclusive with respect to extra radiation, and for which NLO-level results have to be preferred to tree-level merged ones, since they provide one with better predictions for absolute normalisations and for theoretical uncertainties

Summary

Introduction

Present LHC data provide evidence that the scalar particle observed at the LHC is the one predicted by the Brout–Englert– Higgs symmetry breaking mechanism [1,2] of SU(2)L × U (1)Y as implemented in the Standard Model (SM) [2]. We limit ourselves to pointing out that H H production via gluon–gluon fusion is computed at the NLO in a “loop-improved” EFT approach, using the exact one-loop real-emission and improved one-loop virtual matrix elements; that in the case of ttH H and t j H H production exact NLO QCD results are presented in this paper for the first time; and that by matching NLO computations to parton showers we generate samples of events, for the first time, for each of the production channels, which can be used for fully realistic simulations, including those at detector level.

Results

Conclusion