"Figure 3a" of "Search for ttbar resonances in final states with exactly one or two leptons using 140 fb$^{-1}$ of pp collision data at $\sqrt{s}=13$ TeV with the ATLAS experiment"

Distribution of the reconstructed Δφ / π in (a) the signal regions and (b) the validation regions of the 2-lepton channel. Each bin corresponds to one of the signal or validation regions. The distributions and the uncertainty band are obtained before the final fit to the data (pre-fit). "Other Bkg." combines the t̄t + V, t̄t + H, diboson and fakes backgrounds together. In (a), a 3 TeV Z' signal (green dashed and dotted line), a 1 TeV GKK signal (blue dotted line) and a 2 TeV gKK signal (red short-dashed and dotted line) are overlaid for illustration purposes, normalised to the total background. The lower panels show the ratio of the data to the total SM background prediction. The error bands include both the statistical and systematic uncertainties.