Transverse spin asymmetries and the electron Yukawa coupling at an FCC-ee
We show that measurements of single transverse-spin asymmetries at an 𝑒 + 𝑒 − collider can enhance the sensitivity to the electron Yukawa coupling, possibly enabling observation of the Standard Model value for this quantity. We demonstrate that the significance in both the 𝑏$\overline{𝑏}$ and semileptonic 𝑊𝑊 final states can be enhanced by factors of up to 3 compared to inclusive cross-section determinations of this coupling for transversely polarized electrons. If the positrons can be simultaneously longitudinally polarized, even at the level of 30%, the significance can be enhanced by a factor of 5 or more. The method utilizes quantum interference between the Higgs signal and the continuum background and is also applicable in other 𝑊𝑊 and 𝑍𝑍 final states.