Testing parton distribution functions with t -channel single-top-quark production

The production of single top-quarks in the t-channel at hadron colliders imposes strong analytic constraints on parton distribution functions (PDFs) through its double deeply inelastic scattering (DDIS) form. We exploit this to provide novel consistency checks between LO, NLO and NNLO PDF fits and propose to include it as a constraint in future PDF fits. Furthermore, while it is well-known that the b-quark PDF is highly sensitive to the b-quark mass, we show that the treatment of this systematic uncertainty is still incomplete, fragmented or outright missing at the moment. Consequently, we conclude that the b-quark mass uncertainty is the dominant but so far broadly neglected theory uncertainty for this process.