Single-top-quark production in the t-channel at NNLO

A bstract We present a calculation of t -channel single-top-quark production and decay in the five-flavor scheme at NNLO. Our results resolve a disagreement between two previous calculations of this process that found a difference in the inclusive cross section at the level of the NNLO coefficient itself. We compare in detail with the previous calculations at the inclusive, differential and fiducial level including b -quark tagging at a fixed scale μ = m t. In addition, we advocate the use of double deep inelastic scattering (DDIS) scales (μ 2 = Q 2 for the light-quark line and μ 2 = Q 2 + mₜ² m t 2 for the heavy-quark line) that maximize perturbative stability and allow for robust scale uncertainties. All NNLO and NLO⊗NLO contributions for production and decay are included in the on-shell and vertex-function approximation. We present fiducial and differential results for a variety of observables used in Standard Model and Beyond Standard Model analyses, and find an important difference between the NLO and NNLO predictions of exclusive t + n -jet cross sections. Overall we find that NNLO corrections are crucial for a precise identification of the t -channel process.