Off-shell t-channel single-top-quark production at next-to-leading order in QCD in a Standard Model Effective Field Theory

We present the fully differential next-to-leading order (NLO) QCD calculation of t-channel single-top-quark production including off-shell effects in the complex mass scheme, and corrections from new operators arising from a Standard Model Effective Field Theory (SMEFT). We include all relevant SMEFT operators at 1/Lambda² that contribute at NLO in QCD, as well as operators that contribute only at 1/Lambda⁴ that do not interfere with the Standard Model. This expansion allows for a systematic theoretical treatment of physics Beyond the Standard Model, and places context around phenomenologically motivated anomalous right- and left-handed Wtb vector and tensor couplings.

We explore key observables at the LHC, and find shifts in the shape of some jet distributions from off-shell effects that are important for extracting the top-quark mass in the Standard Model. We also find that NLO QCD and off-shell top-quark mass effects are important for angular distributions that are used to search for SMEFT physics. The calculation is publicly available in MCFM-8.3.