Constraining dimension-6 SMEFT with higher-order predictions for $p p \to t W$

Abstract: We study single-top production in association with a $W$ boson at the LHC as a probe of dimension-6 Standard Model Effective Field Theory (SMEFT) at leading order, next-to-leading order, and approximate next-to-next-to-leading order accuracy in QCD. The process is sensitive to operators that modify the top-quark weak and chromomagnetic dipole interactions, and we perform three-parameter linear and quadratic SMEFT fits using doubly differential top-quark distributions in transverse momentum and rapidity for the Run II and Run III configurations at the LHC. We provide a detailed account of the uncertainties and quantify the impact of the different uncertainty components across bins and perturbative orders. We find that effective scales up to 2 TeV can be probed in nonmarginalized fits, while in marginalized fits the corresponding scales are around 0.5 and 1.5 TeV for linear and quadratic fits, respectively.