This paper reports a detailed simulation that asks whether a future electron–positron collider run at the Higgs mass could measure the tiny coupling between the Higgs boson and the electron. The authors study s‑channel Higgs production at a centre‑of‑mass energy of 125 GeV, with the Higgs decaying to a pair of W bosons and one of those W bosons decaying to a charged lepton plus a neutrino and the other to two jets. Using assumed beam conditions and 10 inverse attobarns (10 ab−1) of data, they find a combined statistical significance of 2.0 standard deviations and set an upper limit on the coupling modifier κ_e = y_e / y_e^SM of about 1.35 at 95% confidence level. The electron Yukawa in the Standard Model is extremely small (y_e ≃ 2.9×10^−6), so any direct constraint is noteworthy.

To reach this result the team ran full simulation chains. They generated signal and background events with the Whizard Monte Carlo generator, simulated parton showering and hadron decays with Pythia6, and modeled detector response with Delphes using the IDEA detector configuration. They treated four separate signal categories that cover on‑ and off‑shell W decays and include electrons, muons and leptons from τ decays. A multiclass gradient boosted decision tree was trained to separate the signal from dominant backgrounds using many kinematic and shape variables.

The approach relies on producing the Higgs directly in the s‑channel by tuning the beams to the Higgs mass. That requires a very small spread in the beam energy so the collider “sits” on the Higgs resonance. The authors assume a monochromatized beam energy spread of 4.1 MeV, which, after including initial‑state radiation effects, gives a resonant Higgs production cross section of about 280 attobarns (an attobarn is a tiny unit used to express collision probability). The main backgrounds are continuum WW* production and Z/ Z+X processes, which have production rates many orders of magnitude larger than the signal and are thus hard to suppress.