A detailed study on the prospects for a tt threshold scan in e+e− collisions

A scan of the beam energy across the top quark pair (tt) production threshold is part of the program of future Higgs, top, and electroweak factory projects. In this paper, we provide projections for the achievable precision in the top quark mass (mt), width (Γt), and Yukawa coupling (yt) at the electron-positron (e+e−) stage of the Future Circular Collider (FCC-ee). The study includes a detailed assessment of parametric and systematic uncertainties, as well as a rigorous estimate of the effect of point-to-point correlations. We project that mt and Γt can be determined with an experimental precision of about 6.8 and 11.5 MeV, respectively, when mt is defined in the potential-subtracted (PS) scheme. The impact of theoretical uncertainties due to missing higher orders is found to be of about 35 (25) MeV on mt (Γt) at N3LO in non-relativistic QCD. Therefore, improvements in the theoretical accuracy, which is an active area of development, are key to match the achievable experimental precision at a future e+e− collider. Finally, we explore the prospects for a measurement of yt at FCC-ee via a dedicated run above the tt production threshold.