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

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 <em>μ = m_t</em>. In addition, we advocate the use of double deep inelastic scattering (DDIS) scales (<em>μ² = Q²</em> for the light-quark line and <em>μ² = Q²</em> + <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>m</mml:mi><mml:mi>t</mml:mi><mml:mn>2</mml:mn> </mml:msubsup> </mml:math> 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.