Measurements of $H\rightarrow W^+W^-$ in the Fully Leptonic Decay Mode at the FCC-ee

TL;DR

This study targets the precision measurement of the product σ(e+e− → ZH) × Br(H→WW) in the fully leptonic ZH final state at the FCC-ee, evaluating two run scenarios: sqrt(s)=240 GeV with 10.8 ab^-1 and sqrt(s)=365 GeV with 3.12 ab^-1. Using full MC simulation (Whizard/Kilian, Pythia, Delphes IDEA) and six orthogonal four-lepton channels, the analysis combines cut-based selections with a 44-feature XGBoost BDT to maximize signal significance, aided by the recoil mass discriminator. The CMS Combine framework yields a combined relative uncertainty of 2.9% at 240 GeV (≈35σ) and 6.8% at 365 GeV (≈14.7σ), demonstrating a substantially higher precision at the 240 GeV run. Overall, the work demonstrates the FCC-ee’s capability for high-precision Higgs coupling measurements in a clean environment, with machine learning providing meaningful gains in sensitivity across all leptonic channels.

Abstract

The expected precision on measuring the $σ(e^+ e^- \rightarrow ZH) \times Br(H\rightarrow W^+W^-)$ in the fully leptonic decay mode at the Future Circular Collider (FCC) is presented. We consider two FCC-ee scenarios: $\sqrt{s} =240$ GeV centre-of-mass energy with a luminosity of 10.8$\rm{~ab}^{-1}$ and $\sqrt{s} =365$ GeV centre-of-mass energy with a luminosity of 3.12$\rm{~ab}^{-1}$. Our results indicate that a relative uncertainty of 2.9\% and 6.8\% can be achieved on measurements of $σ(e^+ e^- \rightarrow ZH) \times Br(H\rightarrow W^+W^-)$ in the fully leptonic decay mode at $\sqrt{s} =240$ GeV and $\sqrt{s} =365$ GeV, respectively.

Figures (4)

• Figure 1: Distributions of observables after applying preselection criteria for $\sqrt{s}=240$ GeV. (a) $Z$ candidate mass for the ZeeHemu channel. (b) Recoil mass for the ZmumuHemu channel. (c) $\eta_{\text{miss}}$ for the ZeeHmumu channel. (d) $\cos{\theta_\text{MET}}$ in the ZeeHee channel. (e) energy of the second lepton pair in the ZmumuHee channel. (f) invariant mass of the second lepton pair in the ZmumuHmumu channel. The uncertainty associated with the MC simulation is shown by the shaded area.
• Figure 2: MVA score for the ZmumuHee, ZeeHmumu, ZmumuHmumu, ZeeHee, ZmumuHemu, ZeeHemu channels for $\sqrt{s}=240$ GeV. The uncertainty associated with the MC simulation is shown by the shaded area.
• Figure 3: Distributions of observables after applying preselection criteria for $\sqrt{s}=365$ GeV. (a) $Z$ candidate mass for the ZeeHemu channel. (b) Recoil mass for the ZmumuHemu channel. (c) $\eta_{\text{miss}}$ for the ZeeHmumu channel. (d) $\cos{\theta_\text{MET}}$ in the ZeeHee channel. (e) energy of the second lepton pair in the ZmumuHee channel. (f) invariant mass of the second lepton pair in the ZmumuHmumu channel. The uncertainty associated with the MC simulation is shown by the shaded area.
• Figure 4: MVA score for the ZmumuHee, ZeeHmumu, ZmumuHmumu, ZeeHee, ZmumuHemu, ZeeHemu channels for $\sqrt{s}=365$ GeV. The uncertainty associated with the MC simulation is shown by the shaded area.