Speaker
Description
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.