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

TL;DR

This work delivers comprehensive NLO QCD predictions, matched to parton showers, for all major SM Higgs-pair production channels at the LHC, enabling fully differential event samples and robust uncertainty estimates. By employing a loop-improved EFT for gg→$HH$ and exact one-loop amplitudes elsewhere within MadGraph5_aMC@NLO, the authors provide state-of-the-art predictions across gg→$HH$, VBF, $t\bar t HH$, $WHH$, $ZHH$, and $tjHH$. They demonstrate that NLO corrections reduce theoretical uncertainties and shape dependences, particularly for gluon-initiated processes, while showing consistent shower-to-shower results. These results are vital for precise extraction of the Higgs self-coupling $\lambda$ and for probing possible new physics in Higgs sectors, with ready-to-use samples for phenomenology and experimental analyses.

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.

Figures (7)

• Figure 1: Classes of diagrams for Higgs pair production in hadron hadron collisions: double Higgs production without $HHH$ vertices on the left-hand side, and, on the right-hand side, the contribution due to the Higgs self interaction. Final state particles other than the Higgs bosons are understood.
• Figure 2: Total cross sections at the NLO in QCD for the six largest $HH$ production channels at $pp$ colliders. The thickness of the lines corresponds to the scale and PDF uncertainties added linearly.
• Figure 3: Total cross sections at the LO and NLO in QCD for $HH$ production channels, at the $\sqrt{s}=$14 TeV LHC as a function of the self-interaction coupling $\lambda$. The dashed (solid) lines and light- (dark-)colour bands correspond to the LO (NLO) results and to the scale and PDF uncertainties added linearly. The SM values of the cross sections are obtained at $\lambda/\lambda_{\rm SM}=1$.
• Figure 4: Transverse momentum distribution of the hardest Higgs boson in $HH$ production in the gluon-gluon fusion, VBF, $t \bar{t} HH$, $WHH$ and $ZHH$ channels, at the 14 TeV LHC. The main frame displays the NLO+PS results obtained after showering with Pythia8 (solid) and HERWIG6 (dashes). The insets show, channel by channel, the ratios of the NLO+ Pythia8 (solid), NLO+ HERWIG6 (dashes), and LO+ HERWIG6 (open boxes) results over the LO+Pythia8 results (crosses). The dark-colour (light-colour) bands represent the scale (red) and PDF (blue) uncertainties added linearly for the NLO (LO) simulations.
• Figure 5: As in fig. \ref{['fig:pth1']}, for the softest Higgs bosons.