Study of $Z\gamma$ Events and Limits on Anomalous $ZZ\gamma$ and $Z\gamma \gamma$ Couplings in $p\overline{p}$ Collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We present a measurement of the $Z\gamma$ production cross section and limits on anomalous $ZZ\gamma$ and $Z\gamma \gamma$ couplings for form-factor scales of $\Lambda =750$ and 1000 GeV. The measurement is based on 138 (152) candidates in the $ee\gamma$ ($\mu \mu \gamma$) final state using $320(290){\mathrm{pb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are $|h_{10,30}^Z|<0.23$, $|h_{20,40}^Z|<0.020$, $|h_{10,30}^{\gamma }|<0.23$, and $|h_{20,40}^{\gamma }|<0.019$ for $\Lambda =1000\mathrm{GeV}$.

Figure 1

Photon candidate $E_T$ spectrum for $\ell \ell \gamma$ data (solid circles), QCD multijet background (shaded histogram), the Monte Carlo simulation of the ${\ell }^{+}{\ell }^{-}\gamma$ production with anomalous $ZZ\gamma$ ($h_3=-2.1$, $h_4=0.24$) coupling (dashed histogram), and the standard model plus background (solid histogram). The shaded band is the systematic uncertainty on the SM plus background. The Monte Carlo distribution is normalized to the luminosity.

Figure 2

$\mathrm{\text{Dilepton}}+\mathrm{\text{photon}}$ vs dilepton mass of $Z\gamma$ candidates. Candidates in the electron channel are shown as empty circles, while the muon mode candidates are shown as stars.

Figure 3

(a) Dilepton mass and (b) $\mathrm{\text{dilepton}}+\mathrm{\text{photon}}$ mass of $\ell \ell \gamma$ data (solid circles), QCD multijet background (shaded histogram), and the standard model plus background (histogram). The shaded band is the systematic uncertainty on the SM plus background. The Monte Carlo distribution is normalized to the luminosity.

Figure 4

The 95% C.L. two-dimensional exclusion limits for $CP$-conserving (a) $ZZ\gamma$ and (b) $Z\gamma \gamma$ couplings for $\Lambda =1\mathrm{TeV}$. Dashed lines illustrate the unitarity constraints.