LHC: Standard Higgs and Hidden Higgs

TL;DR

This work addresses how LHC Higgs searches should be interpreted when a visible Higgs mixes with a hidden-sector Higgs through a portal, which alters production and decay probabilities. The authors derive relations tying observable ratios $\mathcal{R}$ and $\mathcal{J}$ to the mixing angle $\chi$ and the hidden width $\Gamma^{\text{hid}}$, with production scaling as $\sigma_{1,2}=\cos^2\chi\,\sigma^{\text{SM}}_{1,2}$ (or $\sin^2\chi$ for the heavier state) and visible/invisible widths including hidden contributions. Using current LHC bounds and LEP limits, they map allowed regions in the $(M_{1,2},\cos^2\chi, \Gamma^{\text{hid}}_1/\Gamma^{\text{SM}}_{\text{tot},1})$ space and discuss implications for a second Higgs $H_2$, including a sum rule $\mathcal{R}_1+\mathcal{J}_1+\mathcal{R}_2+\mathcal{J}_2=1$ to test consistency. The framework provides a coherent interpretation of deviations from SM expectations and, if a Higgs is discovered, a quantitative measure of its SM-likeness and guidance for locating the hidden/heavier partner.

Abstract

Interpretations of Higgs searches critically involve production cross sections and decay probabilities for different analysis channels. Mixing effects can reduce production rates, while invisible decays can reduce decay probabilities. Both effects can transparently be quantified in Higgs systems where a visible Higgs boson is mixed with a hidden sector Higgs boson. Recent experimental exclusion bounds can be re-interpreted in this context as a sign for non-standard Higgs properties. Should a light Higgs boson be discovered, then our analysis will quantify how closely it may coincide with the Standard Model.

Figures (3)

• Figure 1: Bounds on the mixing and hidden decay width of $H_1$ for the point $M_{H_1} = 155$$\text{GeV}; \mathcal{R} = 0.4$ in the standard-hidden Higgs scenario, based on current experimental results HiggsATLASHiggsCMSRol. The regions dappled by small squares are compatible with unitarity and precision measurements. The dot indicates the $\Gamma_1^\text{hid} \to 0$ limit of the exclusion curve at $\mathcal{R}$. The dotted line indicates the projected search limit for $\mathcal{L} = 50~\text{fb}^{-1}$. The corresponding results for $H_2$ with the same mass follow from mirroring all lines at $\cos^2\chi = 1/2$.
• Figure 2: Contours for mixing and hidden decay width of the Higgs boson $H_1$ if visible and invisible ratios of cross sections are measured. The uncertainties of $\mathcal{R}$, shown at 68% CL as shaded band, are determined by means of SFitter sfitter including both experimental and theoretical errors. The uncertainties of $\mathcal{J}$ cannot be reliably estimated at the present time. A currently not excluded Higgs mass of 155 GeV with $\mathcal{R} = \mathcal{J} = 0.4$ is chosen for illustration. The crossing point defines the central values of both parameters. The analysis for $H_2$ runs parallel after replacing $\cos^2\chi \rightarrow \sin^2\chi$.
• Figure 3: 95% CL contours for the mixing and hidden decay width from the observation of a SM-like Higgs boson [$\mathcal{R}=1$] of mass 125 GeV. The uncertainty bands for different LHC energies and luminosities are determined by means of SFitter sfitter including both experimental and theoretical errors. To focus on the SM limit proper, $\{\cos^2\chi,\Gamma^\text{inv}_1\} \to \{1,0\}$, the observable $\Gamma^\text{inv}_1$ is chosen as parameter in the figure.