Multi-parameter fits to the tt̄ threshold observables at a future e⁺e^- linear collider

A realistic study of the physics reach of a tt̄ threshold scan at a future ep+e- linear collider is presented. The results obtained take into account experimental and, to a large extent, theoretical systematic errors, as well as beam effects. Because of the large correlations between the physical parameters that can be extracted from the threshold scan, a multi-parameter fit is seen as mandatory. It is shown that the top mass, the top width and αs,(Mz) can be extracted simultaneously with uncertainties around 20 MeV, 30 MeV and 0.0012, respectively, while the top Yukawa coupling can be measured, with the previous three parameters, to an uncertainty of about 35%, after assuming an external prior on αs of ±0.001.