Search for $Z\gamma$ events with large missing transverse energy in $p\overline{p}$ collisions at $\sqrt{s}\mathbf{=}1.96\mathrm{TeV}$

We present the first search for new phenomena in $Z\gamma$ final states with large missing transverse energy using data corresponding to an integrated luminosity of $6.2{\mathrm{fb}}^{-1}$ collected with the D0 experiment in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. This signature is predicted in gauge-mediated supersymmetry-breaking models, where the lightest neutralino ${\tilde{\chi }}_1^0$ is the next-to-lightest supersymmetric particle and is produced in pairs, possibly through decay from heavier supersymmetric particles. The ${\tilde{\chi }}_1^0$ can decay either to a $Z$ boson or a photon and an associated gravitino that escapes detection. We exclude this model at the 95% C.L. for supersymmetry-breaking scales of $\Lambda <87\mathrm{TeV}$.

Figure 1

Distribution of ${\mathrm{E̸}}_T$ for $Z\gamma$ events in the (a) $ee\gamma$ channel and (b) $\mu \mu \gamma$ channel before requiring ${\mathrm{E̸}}_T$ significance $>5$. The hatching on the sum of background contributions indicates the total uncertainty on the background prediction.

Figure 2

Distribution of BDT output in the $ee\gamma$ channel and $\mu \mu \gamma$ channel for background only, background with a $\Lambda =85\mathrm{TeV}$ signal added, and data. The total background uncertainties are indicated as shaded bands.

Figure 3

Limit on the cross section for $Z\gamma +{\mathrm{E̸}}_T$ production as a function of $\Lambda$ (lower horizontal axis) and $M({\tilde{\chi }}_1^0)$ (upper horizontal axis) at 95% C.L. combined for the $ee\gamma$ and $\mu \mu \gamma$ channels. The NLO cross section for the signal, with a band indicating the parton distribution function uncertainty, is overlaid.