Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the SR (t-pass) and SR (t-fail) after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. A representative mono-top signal (vector coupling scenario) with a mediator mass of 1 TeV, a DM candidate mass of 150 GeV, and a cross section of 1 pb is overlaid as an orange line. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the SR (t-pass) and SR (t-fail) after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. A representative mono-top signal (vector coupling scenario) with a mediator mass of 1 TeV, a DM candidate mass of 150 GeV, and a cross section of 1 pb is overlaid as an orange line. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the W(e$\nu$) (t-pass) and W(e$\nu$) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the W(e$\nu$) (t-pass) and W(e$\nu$) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the W($\mu\nu$) (t-pass) and W($\mu\nu$) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the W($\mu\nu$) (t-pass) and W($\mu\nu$) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the Z(ee) (t-pass) and Z(ee) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the Z(ee) (t-pass) and Z(ee) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the Z($\mu\mu$) (t-pass) and Z($\mu\mu$) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the Z($\mu\mu$) (t-pass) and Z($\mu\mu$) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the t$\bar{t}$ (e$\nu$) (t-pass) and t$\bar{t}$ (e$\nu$) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the t$\bar{t}$ (e$\nu$) (t-pass) and t$\bar{t}$ (e$\nu$) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the tt ($\mu\nu$) (t-pass) and tt ($\mu\nu$) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the tt ($\mu\nu$) (t-pass) and tt ($\mu\nu$) (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the $\gamma$ (t-pass) and $\gamma$ (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Postfit distributions of the magnitude of the hadronic recoil $R_{\mathrm{T}}$ in the $\gamma$ (t-pass) and $\gamma$ (t-fail) CRs after a fit of the background model to the data. The last bin of each distribution also contains events with $R_{\mathrm{T}}$ > 1000 GeV. The background processes are stacked together. The gray band represents the statistical and postfit systematic uncertainties in the predicted background yields after the fit.

Upper limits at 95% CL on $\sigma\mathcal{B}$ of mono-top production presented in the two- dimensional plane spanned by the mediator and DM candidate masses for a mediator mass between 200 and 2250 GeV and a DM candidate mass between 1 and 1125 GeV only consider- ing on-shell decays of the mediator to the DM candidates. The mediator has vector couplings to quarks and DM candidates in the upper plot and axial-vector couplings in the lower plot. The median expected exclusion range is indicated by a black solid line, demonstrating the search sensitivity of the analysis. The 68% probability interval of the expected exclusion is shown in black dashed lines. Contours of theory predictions for constant values of $\sigma\mathcal{B}$ are shown in gray dashed lines. The observed exclusion contour of mediator and DM candidate masses is rep- resented by the red solid line. The exclusion contour obtained from measurements of the DM relic density $\Omega_{\mathrm{nbm}}h^2$ by the Planck Collaboration is shown in the gray solid line.

Upper limits at 95% CL on $\sigma\mathcal{B}$ of mono-top production presented in the two- dimensional plane spanned by the mediator and DM candidate masses for a mediator mass between 200 and 2250 GeV and a DM candidate mass between 1 and 1125 GeV only consider- ing on-shell decays of the mediator to the DM candidates. The mediator has vector couplings to quarks and DM candidates in the upper plot and axial-vector couplings in the lower plot. The median expected exclusion range is indicated by a black solid line, demonstrating the search sensitivity of the analysis. The 68% probability interval of the expected exclusion is shown in black dashed lines. Contours of theory predictions for constant values of $\sigma\mathcal{B}$ are shown in gray dashed lines. The observed exclusion contour of mediator and DM candidate masses is rep- resented by the red solid line. The exclusion contour obtained from measurements of the DM relic density $\Omega_{\mathrm{nbm}}h^2$ by the Planck Collaboration is shown in the gray solid line.