Could electron-top interactions spoil the measurement of the Higgs trilinear? -A quantitative estimate at future lepton colliders-

TL;DR

This paper assesses how electron-top interactions could impact the precision measurement of the Higgs self-coupling at future lepton colliders, finding effects are small but significant for accurate determination.

Contribution

It provides a quantitative estimate of the influence of electron-top contact interactions on Higgs self-coupling measurements at FCC-ee, highlighting their limited but non-negligible impact.

Findings

Electron-top interactions affect Higgs self-coupling sensitivity below 1%.

Sensitivity remains around 17% at 1σ confidence level.

Fermion pair production measurements are crucial for analysis.

Abstract

The measurement of the Higgs self-coupling is considered the next milestone in the study of the Higgs boson properties. At future $e^+e^-$ facilities below the double Higgs production threshold, this is extracted from the $Zh$ production cross-section, which is sensitive to the trilinear coupling at the one-loop level. At the same perturbative order, potential effects beyond the Standard Model (SM) may affect the Higgstrahlung rate and distort the self-coupling determination. We study the question focusing especially on contact interactions containing two electron and two top-quark fields. We conclude that, in the context of FCC-ee and its planned runs at different energies, $eett$ interactions change the Higgs self-coupling sensitivity below the percent level. Even in the most pessimistic scenarios, we confirm a robust sensitivity of the order of 17% at the 1$\sigma$ confidence level under the assumption of otherwise SM-like Higgs couplings. A crucial role in these results is played by the measurement of fermion pair production above the $Z$ resonance.