Precision Measurements of Higgs Hadronic Decay Modes at the FCC-ee

TL;DR

The paper presents a comprehensive FCC-ee study of Higgs hadronic decays, combining Higgs-strahlung and VBF measurements at $\sqrt{s}=240$ and $365$ GeV to determine $\sigma\times\mathcal{B}$ for $H\to b\bar{b}$, $c\bar{c}$, $s\bar{s}$, and $gg$. It leverages the IDEA detector concept with advanced flavor tagging and a global, covariance-aware fit across three final states ($\ell\ell jj$, $\nu\bar{\nu}jj$, $jjjj$), including a full interference treatment in $\nu\bar{\nu}jj$. The study demonstrates percent-to-permil level precision for the dominant hadronic modes and establishes sensitivity to the rare $H\to s\bar{s}$ decay, enabling potential evidence of the strange-quark Yukawa coupling. By combining measurements at two energies with a robust statistical framework, it provides essential inputs for model-independent Higgs-coupling fits and the extraction of the total Higgs width at FCC-ee.

Abstract

The expected precision at the FCC-ee on the product $σ\times\mathcal{B}(H\rightarrow b\bar{b}, c\bar{c},s\bar{s},gg)$ of Higgs boson production cross sections times branching ratios of hadronic decays is presented. This study provides the first comprehensive determination of all major hadronic Higgs decay modes in a combined fit at future $e^+ e^-$ colliders, using both Higgs-strahlung ($ZH$) and Vector boson fusion ($ν\barν H$) production processes, with a full treatment of interference effects in the $ν\barν jj$ final state. It assumes four identical IDEA detectors collecting $e^+e^-$ collisions at $\sqrt{s}=240$ and $365\,$GeV. The combination of all channels across both energies, with full covariance between production and decay modes, yields a production cross-section times branching-ratio precision at the percent to per-mil level for the dominant hadronic final states ($b\bar{b}, c\bar{c},gg$). These results provide a comprehensive input to the determination of Higgs coupling projections at the FCC-ee, and they establish for the first time sensitivity to the rare decay $H\rightarrow s\bar{s}$, demonstrating that FCC-ee has the potential to provide evidence of the strange-quark Yukawa coupling.

Figures (11)

• Figure 1: Recoil mass distribution of signal and background superimposed after the final selection for (a) $\sqrt{s}=240\,\mathrm{GeV}$ and (b) $\sqrt{s}=365\,\mathrm{GeV}$.
• Figure 2: Confusion matrix of the NN after the final training, evaluated on the validation subsample, for (a) $\sqrt{s}\xspace=240$ GeV and (b) $\sqrt{s}\xspace=365$ GeV.
• Figure 3: The $m_{\mathrm{recoil}}$ and the di-jet invariant mass $m_{jj}$ distributions after pre-selection for the $ZH$ production mode (a,b) and for the VBF production mode (c,d) at $\sqrt{s}=240\,\textrm{GeV}$.
• Figure 4: The $m_{\mathrm{recoil}}$ and the di-jet invariant mass $m_{jj}$ distributions after pre-selection for the $ZH$ production mode (a,b) and for the VBF production mode (c,d) at $\sqrt{s}=365\,\textrm{GeV}$.
• Figure 5: Migration matrix in the four categories of interest, for the $\nu\bar{\nu}\xspace jj$ analysis at $\sqrt{s}=240$ GeV. The numbers correspond to the fraction of events (in percent) of a given process (vertical axis) after the preselection, that are classified in one of the four $K$-like categories (horizontal axis).