Searching the inclusive $\ell \gamma {\mathrm{E̸}}_T+b$-quark signature for radiative top quark decay and non-standard-model processes

We compare the inclusive production of events containing a lepton ($\ell$), a photon ($\gamma$), significant transverse momentum imbalance (${\mathrm{E̸}}_T$), and a jet identified as containing a $b$-quark, to SM predictions. The search uses data produced in proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$ corresponding to $1.9{\mathrm{fb}}^{-1}$ of integrated luminosity taken with the CDF detector. We find 28 $\ell \gamma b{\mathrm{E̸}}_T$ events versus an expectation of ${31.0}_{-3.5}^{+4.1}$ events. If we further require events to contain at least three jets and large total transverse energy, the largest SM source is radiative top-quark pair production, $t\overline{t}+\gamma$. In the data we observe 16 $t\overline{t}\gamma$ candidate events versus an expectation from SM sources of ${11.2}_{-2.1}^{+2.3}$. Assuming the difference between the observed number and the predicted non-top-quark total of ${6.8}_{-2.0}^{+2.2}$ is due to SM top-quark production, we estimate the $t\overline{t}\gamma$ cross section to be $0.15\pm 0.08\mathrm{pb}$.

Figure 1

The distributions for events in the $\ell \gamma b{\mathrm{E̸}}_T$ sample (points) in (a) the $E_T$ of the lepton; (b) the $E_T$ of the photon; (c) the $E_T$ of the most energetic $b$-jet in an event; and (d) the missing transverse energy. The histograms show the estimated SM contributions from radiative top quark decay ($t\overline{t}\gamma$), $WZ$ production, $W\gamma$ production with heavy flavor (HF), $\tau$ leptons, electrons, and jets misidentified as photons, mistagged light-quark and gluon jets, and jets misidentified as leptons (QCD).

Figure 2

The distributions for events in the $\ell \gamma b{\mathrm{E̸}}_T$ sample (points) in (a) the total number of jets; (b) the total transverse energy $H_T$ for the $\ell \gamma b{\mathrm{E̸}}_T$ events. The histograms show the estimated SM contributions from radiative top-quark decay ($t\overline{t}\gamma$), $WZ$ production, $W\gamma$ production with heavy flavor (HF), $\tau$ leptons, electrons, and jets misidentified as photons, mistagged light-quark and gluon jets, and jets misidentified as leptons (QCD).

Figure 3

The distributions for events in the $t\overline{t}\gamma$ sample (points) in (a) the $E_T$ of the lepton; (b) the $E_T$ of the photon; (c) the $E_T$ of the most energetic $b$-jet in an event; and (d) the missing transverse energy, ${\mathrm{E̸}}_T$. The histograms show the estimated SM contributions from radiative top-quark decay ($t\overline{t}\gamma$), $WZ$ production, $W\gamma$ production with heavy flavor (HF), $\tau$ leptons, electrons, and jets misidentified as photons, mistagged light-quark and gluon jets, and jets misidentified as leptons (QCD).

Figure 4

The distributions for events in the $t\overline{t}\gamma$ sample (points) in (a) the total number of jets; (b) the total transverse energy $H_T$ for the $\ell \gamma b{\mathrm{E̸}}_T$ events. The histograms show the estimated SM contributions from radiative top-quark decay ($t\overline{t}\gamma$), $WZ$ production, $W\gamma$ production with heavy flavor (HF), $\tau$ leptons, electrons, and jets misidentified as photons, mistagged light-quark and gluon jets, and jets misidentified as leptons (QCD).

Figure 5

The $\eta -\varphi$ plot of a $t\overline{t}\gamma$ candidate event, in which the energies deposited in the calorimeter towers are displayed in the $\eta -\varphi$ plane. The reconstructed top-quark mass is 167 GeV; the photon $E_T$ is 12 GeV.

Figure 6

Estimate of ${\sigma }_{t\overline{t}\gamma }$ compared with SM expectations and other SM cross sections ${\sigma }_{W^{\pm }\to {\ell }^{\pm }\nu }$, ${\sigma }_{Z\to {\ell }^{+}{\ell }^{-}}$ and ${\sigma }_{t\overline{t}}$ [32].