We investigate the potential of single-spin components of the spin-density matrix in the e+e−→ttˉ process at a future FCC-ee for probing heavy new physics parametrized using the SMEFT framework. We consider the full spectrum of spin observables and the complete angular decomposition of the ttˉ production process in our study. We find that single-spin measurements generically provide stronger probes of SMEFT Wilson coefficients than measurements where the ttˉ spins are correlated, and that single-spin observables are important for resolving flat directions that can appear in the Wilson-coefficient parameter space.
@article{arxiv.2511.01994,
title = {Single-spin measurements and heavy new physics in the $e^+e^- \to t\bar{t}$ process at an FCC-ee},
author = {Haotian Cao and Frank Petriello},
journal= {arXiv preprint arXiv:2511.01994},
year = {2026}
}