Search for single production of vector-like quarks decaying into Wb in pp collisions at sqrt(s) = 13 TeV with the ATLAS detector

A search for singly produced vector-like quarks Q, where Q can be either a T quark with charge +2/3 or a Y quark with charge −4/3, is performed in proton– proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 36.1 fb−1, recorded with the ATLAS detector at the LHC in 2015 and 2016. The analysis targets Q → W b decays where the W boson decays leptonically. No significant deviation from the expected Standard Model background is observed. Upper limits are set on the QW b coupling strength and the mixing between the Standard Model sector and a singlet T quark or a Y quark from a (B, Y ) doublet or a (T, B, Y ) triplet, taking into account the interference effects with the Standard Model background. The upper limits set on the mixing angle are as small as |sin θL| = 0.18 for a singlet T quark of mass 800 GeV, |sin θR| = 0.17 for a Y quark of mass 800 GeV in a (B, Y ) doublet model and |sin θL| = 0.16 for a Y quark of mass 800 GeV in a (T, B, Y ) triplet model. Within a (B, Y ) doublet model, the limits set on the mixing parameter |sin θR| are comparable with the exclusion limits from electroweak precision observables in the mass range between about 900 GeV and 1250 GeV.