Higgs-Pair Production and Measurement of the Triscalar Coupling at LHC(8,14)

TL;DR

The paper studies measuring the Higgs triscalar coupling $\lambda^{hhh}$ via Higgs-pair production in proton collisions $gg\to hh$ at LHC energies $8$ and $14$ TeV. It uses loop-amplitude calculations embedded in MADGRAPH with a next-to-leading-order K-factor $K=1.88$ to simulate $gg\to hh$, explores deviations of $\lambda^{hhh}$ from its SM value, and analyzes final states with decays $hh\to b\bar{b}\gamma\gamma$ as the most promising channel. A cut-based and a multivariate analysis (MVA) are employed; the MVA forms a discriminant from multiple kinematic observables and yields higher sensitivity, enabling a matrix-element fit to the differential distribution $d\sigma/dM_{hh}$ to extract $\lambda^{hhh}$. At LHC14 with $3\,\mathrm{ab}^{-1}$, the SM coupling could be measured with about 40% uncertainty, while non-SM values yield 25–80% uncertainty; the 7–8 TeV data could probe large deviations $\lambda^{hhh}/\lambda^{hhh}_{SM}\gtrsim 7.5$ at 95% CL. The study identifies a zero in the amplitude and a minimum in the distribution near $\lambda^{hhh} \approx 2.45\,\lambda^{hhh}_{SM}$ and concludes that the $b\bar{b}\gamma\gamma$ channel is the most viable for this measurement, with MVAs providing a substantial sensitivity gain over cut-based approaches.

Abstract

We simulate the measurement of the triscalar Higgs coupling at LHC(8,14) via pair production of h(125 GeV). We find that the most promising hh final state is bb gamma gamma. We account for deviations of the triscalar coupling from its SM value and study the effects of this coupling on the hh cross-section and distributions with cut-based and multivariate methods. Our fit to the hh production matrix element at LHC(14) with 3 ab^-1 yields a 40% uncertainty on this coupling in the SM and a range of 25-80% uncertainties for non-SM values.

Figures (7)

• Figure 1: Feynman diagrams which contribute to Higgs boson pair production via gluon fusion.
• Figure 2: Production cross section for $gg\to hh$ at the LHC with $\sqrt s =$ 8 TeV and 14 TeV.
• Figure 3: Amplitude zero in $gg\to hh$ fusion versus $M_{hh}$ for $\lambda^{hhh}/\lambda^{hhh}_{\rm SM} =$ 2.45. The SM value is $\lambda^{hhh}_{SM} = 192$ GeV.
• Figure 4: The differential cross section versus $M_{hh}$ for $\lambda^{hhh}/\lambda^{hhh}_{\rm SM} =$ 1,2,3.
• Figure 5: Signal acceptance for the $b\bar{b} \gamma\gamma$ channel at various cut levels. The reduced acceptance for large values of $\lambda^{hhh}$ correspond to a lower $p_T(h)$