"Figure 4a" of "Search for the single production of vector-like quarks decaying into a W boson and a b quark using single-lepton final states in proton-proton collisions at $\sqrt{s}$ = 13 TeV"

The 95% CL upper limit on the VLQ single-production cross section as a function of mVLQ. The solid black curve gives the observed upper limit, while the dotted black curve shows the expected upper limit, with the green and yellow bands representing the +/-1 and +/-2 standard deviation uncertainties in the expected limit, respectively. The solid red curve displays the theoretical prediction for the Y and T quark single-production cross section assuming exclusive decay to Wb and kappaW = 0.15. This curve also corresponds to the predictions for the T singlet, with B(Wb) = 50% and kappaW = 0.21. The black dashed and dot-dashed curves show the expected cross sections corresponding to a fixed VLQ width to mass ratio Γ/m = 10% for the T singlet and Y quarks, respectively. Below these curves, the VLQ natural width is smaller than the experimental invariant mass resolution, and the narrow-width approximation assumed in the analysis is justified.