Model-independent ZH production cross section at FCC-ee

TL;DR

This work demonstrates a model-independent strategy to measure the $ZH$ production cross section at the FCC-ee using the recoil-mass technique across $ ooted$ energies. By combining $Z$ decays to $e^+e^-$, $fm^+$, and $qar{q}$ with a common leptonic selection and an orthogonal hadronic selection, and applying boosted decision trees to enhance signal from backgrounds, the analysis extracts $\sigma_{ZH}$ with per-mille-level precision. Dedicated bias tests show that the result is robust against variations in Higgs decay modes within the quoted uncertainties, validating model independence at the projected precision. The final combined precision reaches about $0.31 ext{--}0.52 ext{%}$ depending on energy, establishing the most precise projected determination of $ ext{ZH}$ production at future lepton colliders and enabling model-independent determinations of Higgs couplings through global fits.

Abstract

This paper presents prospects for a model-independent measurement of the $ZH$ production cross section at the FCC-ee using the recoil-mass technique at center-of-mass energies of $\sqrt{s}=240$ and $365$ GeV. The analysis considers the muon, electron, and hadronic decay modes of the associated $Z$ boson. Event selections rely primarily on the kinematic properties of the reconstructed $Z$ decay products, ensuring maximal independence from specific Higgs boson decay modes, while multivariate techniques are employed to further enhance sensitivity. Statistical interpretations of the individual final states yield relative precisions of $0.52\%$ for the combined leptonic channels and $0.38\%$ for the hadronic channel at $\sqrt{s}=240$ GeV with an integrated luminosity of $10.8$ ab$^{-1}$. Their full statistical combination leads to total uncertainties of $0.31\%$ at $\sqrt{s}=240$ GeV and $0.52\%$ at $\sqrt{s}=365$ GeV with $3.12$ ab$^{-1}$. Dedicated statistical tests demonstrate model independence at the level of the obtained precision. This study presents, for the first time, a consistent and combined analysis of the leptonic and hadronic final states, achieving the most precise projected determination of the $ZH$ production cross section at future lepton colliders, with model independence demonstrated within the statistical precision.

Figures (10)

• Figure 1: Tree-level diagrams of the Higgs production processes at $\sqrt{s}\xspace = 240 \text{ and } 365\xspace\text{GeV}\xspace$: the $\text{ZH}$ Higgsstrahlung process (left) and the $\nu_e\bar{\nu_e}\text{H}$ fusion process (right).
• Figure 2: Result of the jet clustering: choice of the jet clustering algorithm (top) and jet multiplicity distribution when inclusive clustering is applied (bottom), shown for different Higgs decay modes (left, center) and for the backgrounds (right). The Higgs decays are grouped according to similar decay topologies, which lead to a comparable clustering outcome.
• Figure 3: Event selection cut flow at $\sqrt{s}\xspace = 240\xspace\text{GeV}\xspace$ for the muon (left) and hadronic (right) final states. The signal process corresponds to the $\text{Z}(\mathrm{\mu^{+}\mu^{-}})\text{H}$ and $\text{Z}(\mathrm{q\bar{q}})\text{H}$ processes, respectively.
• Figure 4: Recoil mass distributions for the muon final state at $\sqrt{s}\xspace = 240\xspace\text{GeV}\xspace$ (left) and $\sqrt{s}\xspace = 365\xspace\text{GeV}\xspace$ (right), after the baseline selections, showing both signal and background contributions.
• Figure 5: Selection efficiencies for different Higgs decay modes at $\sqrt{s}\xspace = 240\xspace\text{GeV}\xspace$ for the muon (left) and hadronic (right) final states. The signal corresponds to $\text{Z}(\mathrm{\mu^{+}\mu^{-}})\text{H}$ and $\text{Z}(\mathrm{q\bar{q}})\text{H}$, respectively.