Descoped and Upscoped FCC-ee Running Scenarios in the SMEFT

Abstract

We present projections for the sensitivity to new physics of descoped and upscoped FCC-ee scenarios in the framework of the Standard Model Effective Field Theory (SMEFT). Starting from the baseline FCC-ee programme, we analyse the subsequent impact of, first, removing the top-quark run, then reducing the beam power from 50 MW to 30 MW, and finally removing two interaction points (IPs), in all cases propagating the resulting loss in top-quark mass precision through increased parametric uncertainties. We also analyse the possibility of a staged top-quark run, where the top-quark run is partially restored in case funding becomes available only at a later stage. Motivated by the trade-off between beam power and operational costs, we also consider two upscoped scenarios, either through a uniform increase in luminosity across all energy runs, or through a luminosity enhancement targeting exclusively the top-quark run. We explore the sensitivity and limitations of each scenario and highlight in particular the complementarity between the FCC-ee projections and the (HL)-LHC measurements. By comparing the physics impact of the different running scenarios with the FCC-ee baseline, we show explicitly the importance of the top-quark run, indicating that a substantial fraction of the FCC-ee physics potential depends on it.