Probing the electron Yukawa coupling via resonant Higgs boson production at FCC-ee via e⁺e⁻ → H → WW^* in lepton-plus-jets final states

We report a detailed simulation study of the search for s-channel Higgs boson production in e⁺e⁻ collisions at a center-of-mass (c.m.) energy of √s=125\,GeV at the CERN Future Circular Collider (FCC-ee), as a means to constrain the electron Yukawa coupling, yₑ. The process of interest is e⁺e⁻→ H→ WW^*→ ^±ν+ jj with four different WW^* final states considered, involving both on- and off-shell W bosons decaying either into dileptons (^± = e^± and μ^±, including those from τ^± decays) or into dijets ($jj$). Signal and background events are discriminated through a multiclass gradient boosted decision tree exploiting a comprehensive set of kinematic and topological variables across the four final-state categories. Assuming a monochromatized c.m. energy spread of 4.1 MeV, yielding a σe⁺e⁻→ H = 280\,ab resonant cross section, and an integrated luminosity of 10\,ab⁻¹, the analysis achieves a combined statistical significance of 2.0 standard deviations. This corresponds to an upper limit on the coupling modifier κₑ = yₑ/yₑSM 1.35 at 95% confidence level, and provides the most stringent constraint on the electron Yukawa coupling achieved in simulation-based studies to date.