Researchers have evaluated the impact of different operational scenarios for the future electron-positron collider (FCC-ee) on its ability to detect new physics, using the Standard Model Effective Field Theory (SMEFT) framework. The study analyzes how modifications to the running program, such as the removal or reduction of the top-quark production phase, a decrease in beam power, or a reduction in interaction points, affect measurement precision and, consequently, sensitivity to phenomena beyond the Standard Model. This analysis is crucial for optimizing the design and operational strategy of the FCC-ee, a key project for particle physics in the coming decades.

The study started from the baseline FCC-ee program and considered several "descoped" scenarios, including the suppression of the top-quark phase, a decrease in beam power from 50 MW to 30 MW, and a reduction from four to two interaction points. Each modification was evaluated for its impact on parametric precision, especially the top-quark mass, and how this translates into reduced sensitivity to new physics. "Upscoped" scenarios were also explored, where luminosity is increased, either uniformly across all energies or specifically in the top-quark phase, seeking a balance between scientific potential and operational costs. Complementarity with (HL)-LHC data was an important factor in the evaluation.

The results highlight the critical importance of the top-quark production phase for the FCC-ee's discovery potential. A substantial fraction of the collider's ability to explore new physics directly depends on this phase. The study also considered the possibility of a staged implementation of the top-quark phase, should funding become available later. These projections are fundamental for decision-making regarding the final configuration and operational timeline of the FCC-ee, ensuring that its scientific return in the search for fundamental answers in particle physics is maximized.