Effective field theory analysis of double Higgs production via gluon fusion

TL;DR

This paper analyzes double Higgs production via gluon fusion within an effective field theory framework, using the hh -> bbγγ channel to simultaneously constrain a broad set of EFT operators beyond the Higgs trilinear coupling. It emphasizes the importance of differential information, particularly the hh invariant mass, and investigates the role of dimension-8 operators and jet substructure in extending sensitivity at a future 100 TeV collider. Through detailed simulations, background modeling, and a Bayesian fit across multiple collider scenarios, the authors find that the Higgs trilinear coupling xct are constrained to roughly 30% at FCC100 with 3 ab^-1, but only at O(1) precision at the HL-LHC, and that a careful, exclusive m_hh-binned analysis with proper marginalization over other EFT coefficients substantially weakens optimistic prior estimates. The work also demonstrates that jet substructure can substantially improve sensitivity to energy-growing operators at high m_hh, guiding future multi-channel EFT analyses.

Abstract

We perform a detailed study of double Higgs production via gluon fusion in the Effective Field Theory (EFT) framework where effects from new physics are parametrized by local operators. Our analysis provides a perspective broader than the one followed in most of the previous analyses, where this process was merely considered as a way to extract the Higgs trilinear coupling. We focus on the $hh \to b\bar bγγ$ channel and perform a thorough simulation of signal and background at the 14 TeV LHC and a future 100 TeV proton-proton collider. We make use of invariant mass distributions to enhance the sensitivity on the EFT coefficients and give a first assessment of the impact of jet substructure techniques on the results. The range of validity of the EFT description is estimated, as required to consistently exploit the high-energy range of distributions, pointing out the potential relevance of dimension-8 operators. Our analysis contains a few important improvements over previous studies and identifies some inaccuracies there appearing in connection with the estimate of signal and background rates. The estimated precision on the Higgs trilinear coupling that follows from our results is less optimistic than previously claimed in the literature. We find that a ~30% accuracy can be reached on the trilinear coupling at a future 100 TeV collider with 3 ab^-1. Only an O(1) determination seems instead possible at the LHC with the same amount of integrated luminosity.

Figures (21)

• Figure 1: Cartoon of the region in the plane $(g_*, \lambda/g_*)$, defined by Eqs. (\ref{['eq:ineq1']}),(\ref{['eq:ineq2']}), that can be probed by an analysis including only dimension-6 operators (in white). No sensible effective field theory description is possible in the gray area ($\lambda < g_{min}$), while exploration of the light blue region ($g_{min} < \lambda < \sqrt{g_* g_{min}}$) requires including the dimension-8 operators.
• Figure 2: Feyman diagrams contributing to double Higgs production via gluon fusion (an additional contribution comes from the crossing of the box diagram). The last diagram on the first line contains the $\bar{t} t hh$ coupling, while those in the second line involve contact interactions between the Higgs and the gluons denoted with a cross.
• Figure 3: Differential cross sections obtained by including only the contribution of $M_0$ (dashed blue curve) or $M_2$ (dotted orange curve) in the SM, as functions of $\cos\theta$. Both curves are normalized to the total SM cross section. The partonic center-of-mass energy has been fixed to $\sqrt{\hat{s}}=400\,$GeV in the left plot and to $\sqrt{\hat{s}}=700\,$GeV in the right plot.
• Figure 4: Isocontours of the ratio $r = \sigma_{gD2}/\sigma_{tot}$, defined in the text, in the plane $(m_{hh}, \cos\theta_{min})$.
• Figure 5: Left plot: Normalized differential cross section for $pp \to hh$ in the SM as a function of the invariant mass of the two Higgs bosons. The solid and dotted lines correspond respectively to $\sqrt{s} = 14$ and $100\,$TeV. Right plot: Same as on the left but with logarithmic scale.