Constraints on SMEFT operators from $Z \to \mu \mu bb$ decay

TL;DR

This paper investigates constraints on SMEFT operators from the decay process Z to muons and bottom quarks, using detailed simulations and statistical analysis to derive novel limits on flavor-specific four-fermion interactions.

Contribution

It provides the first process-specific limits on flavor-resolved four-fermion SMEFT operators involving muons and bottom quarks from Z decays.

Findings

Derived constraints on dimension-six SMEFT operators affecting Z to mu mu bb decays.

Implemented state-of-the-art Monte Carlo simulations including detector effects.

Provided the first limits on flavor-specific four-fermion operators involving muons and bottom quarks.

Abstract

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 $Z \to \mu\mu bb$ 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.