The Standard Model Effective Field Theory (SMEFT) provides a systematic framework to probe indirect effects of heavy new physics via precision measurements. While SMEFT constraints have been extensively studied using purely leptonic Z decays and inclusive Z production, mixed leptonic-hadronic modes remain largely unexplored. In this work, we analyze Z→μμbb decays within the SMEFT framework, deriving constraints on dimension-six operators that affect four-fermion interactions between leptons and bottom quarks, as well as Z-fermion couplings. Signal and background events are simulated with state-of-the-art Monte Carlo tools, including detector effects such as b-tagging, and limits on the relevant Wilson coefficients are extracted using kinematic distributions and a profile likelihood approach. Our results provide complementary constraints to existing SMEFT studies and yield the first process-specific limits on flavor-resolved four-fermion operators involving muons and bottom quarks from Z decays.
@article{arxiv.2512.23226,
title = {Constraints on SMEFT operators from $Z \to \mu \mu bb$ decay},
author = {Zijian Wang and Tianyi Yang and Tianyu Mu and Andrew Levin and Qiang Li},
journal= {arXiv preprint arXiv:2512.23226},
year = {2026}
}