Probing the CP violation effects via the angular coefficients in Drell-Yan production

Abstract

The naive-$T$-odd angular coefficients $A_5$--$A_7$ in Drell--Yan production are highly suppressed in the Standard Model (SM), making them sensitive probes of CP-violating interactions beyond the SM. We study these observables within the Standard Model Effective Field Theory (SMEFT), focusing on dimension-six electroweak and chromomagnetic quark dipole operators. Due to their chirality-flipping structure, the leading contributions from CP-violating dipole interactions arise at $\mathcal{O}(1/Λ^4)$ through the interference between electroweak and chromomagnetic dipole amplitudes. We find that the sensitivity is primarily driven by $A_6$ and $A_7$ in the high dilepton transverse momentum region, where the dipole contributions are enhanced, while $A_5$ remains largely insensitive. Combining the ATLAS and CMS measurements, we constrain the CP-violating dipole combinations of Wilson coefficients at the $\mathcal{O}(0.1)$ level for $Λ=1~{\rm TeV}$. Assuming statistically dominated uncertainties at the HL-LHC, the sensitivity can be improved to the $\mathcal{O}(10^{-3})$ level. Our results highlight $A_6$ and $A_7$ as complementary probes of CP-violating dipole interactions at hadron colliders.