Higgs pair production in the NMSSM at the LHC

TL;DR

This work investigates Higgs-pair production in the NMSSM in a scenario where a light, singlet-like $H_1$ lies below $M_{H_2}\approx125$ GeV, while the SM-like $H_2$ sits near $125$ GeV. Using NMSSMTools for the spectrum and trilinear couplings and a modified HPAIR for gluon-fusion cross sections with leading stop/top corrections, the authors scan a representative NMSSM parameter space under constraints from Higgs data and impose $M_{H_1}>65$ GeV to avoid on-shell $H_2\to H_1H_1$ decays. They find that the sum of cross sections for all Higgs-pair final states is never below the SM expectation and can reach up to about $2.5\times$ the SM value for $M_{H_1}\gtrsim100$ GeV, with notable enhancements in the $b\bar{b}+\gamma\gamma$ channel due to favorable $H_2\to\gamma\gamma$ and $H_1$ contributions. However, in some parameter regions the rates involving $H_1$ can be too small to detect, making observation rely on direct production or decays of heavier states, and underscoring the need for flexible dihiggs analyses to probe a light NMSSM Higgs at the LHC.

Abstract

In the NMSSM it is well possible to find an additional Higgs boson with a mass below 125 GeV which remains invisible in standard Higgs boson search channels. We study the Higgs pair production cross sections times branching fractions in this scenario, focusing on gluon fusion and the bb+tautau and bb+gammagamma final states. Summing over the SM-like and the lighter Higgs states, the production cross sections times branching fractions are never below the ones for SM Higgs pair production. Sizable enhancements of the signal rates are also possible, notably if a lighter Higgs state is produced. However, the rates involving at least one lighter Higgs boson are not always sufficiently large to guarantee its discovery.

Figures (4)

• Figure 1: Scatter plots of the trilinear Higgs couplings $g(H_2,H_2,H_2)$ (top left), $g(H_1,H_2,H_2)$ (top right), $g(H_1,H_1,H_2)$ (bottom left) and $g(H_1,H_1,H_1)$ (bottom right) as function of $M_{H_1}$.
• Figure 2: The Higgs pair production cross sections relative to the SM for the final states $H_2+H_2$ (top left), $H_2+H_1$ (top right), $H_1+H_1$ (bottom left) and the sum over all final states (bottom right).
• Figure 3: The Higgs pair production cross sections relative to the SM for the final states $H_2+H_2 \to b\bar{b}+\tau^+\tau^-$ (top left), $H_2+H_1 \to b\bar{b}+\tau^+\tau^-$ (top right), $H_1+H_1 \to b\bar{b}+\tau^+\tau^-$ (bottom left) and the sum over all $H_i$ into $b\bar{b}+\tau^+\tau^-$ (bottom right).
• Figure 4: The Higgs pair production cross sections relative to the SM for the final states $H_2+H_2 \to b\bar{b}+\gamma\gamma$ (top left), $(H_1 \to b\bar{b})+(H_2\to \gamma\gamma)$ (top right), $(H_1 \to \gamma\gamma) +(H_2\to b\bar{b})$ (middle left), $H_1+H_1 \to b\bar{b}+\gamma\gamma$ (middle right) and the sum over all $H_i$ into $b\bar{b}+\gamma\gamma$ (bottom).