$Z_{\gamma }$ production and limits on anomalous $Z{Z}_{\gamma }$ and $Z_{\gamma \gamma }$ couplings in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We present a measurement of $p\overline{p}\to Z\gamma \to {\ell }^{+}{\ell }^{-}\gamma$ ($\ell =e$, $\mu$) production with a data sample corresponding to an integrated luminosity of $6.2{\mathrm{fb}}^{-1}$ collected by the D0 detector at the Fermilab Tevatron $p\overline{p}$ Collider. The results of the electron and muon channels are combined, and we measure the total production cross section and the differential cross section $d\sigma /d{p}_T^{\gamma }$, where $p_T^{\gamma }$ is the momentum of the photon in the plane transverse to the beam line. The results obtained are consistent with the standard model predictions from next-to-leading order calculations. We use the transverse momentum spectrum of the photon to place limits on anomalous $ZZ\gamma$ and $Z\gamma \gamma$ couplings.

Figure 1

Feynman diagrams for leading-order $Z\gamma$ production in the SM: (a) and (b) initial-state radiation from one of the initial-state partons; (c) and (d) final-state radiation from one of the final-state leptons.

Figure 2

Feynman diagrams illustrating anomalous $Z\gamma$ production with a $ZZ\gamma$ vertex (a) and a $Z\gamma \gamma$ vertex (b).

Figure 3

Unfolded $d\sigma /d{p}_T^{\gamma }$ distribution with no $M_{\ell \ell \gamma }$ requirement for combined electron and muon data compared to the NLO mcfm prediction.

Figure 4

Unfolded $d\sigma /d{p}_T^{\gamma }$ distribution with $M_{\ell \ell \gamma }>110\mathrm{GeV}/c^2$ for combined electron and muon data compared with the NLO mcfm prediction.

Figure 5

The SM prediction and anomalous $Z\gamma$ coupling production compared with the unfolded $d\sigma /d{p}_T^{\gamma }$ for combined muon and electron channels for $p_T^{\gamma }>30\mathrm{GeV}/c$ and $M_{\ell \ell \gamma }>110\mathrm{GeV}/c^2$.

Figure 6

The 2D (contour) and 1D (cross) limits on the anomalous coupling parameters for (a) $ZZ\gamma$ and (b) $Z\gamma \gamma$ vertices at the 95% C.L. for $\Lambda =1.2\mathrm{TeV}$. Limits on $S$-matrix unitarity are represented by the dotted lines.

Figure 7

The 2D (contour) and 1D (cross) limits on the anomalous parameters for (a) $ZZ\gamma$ and (b) $Z\gamma \gamma$ vertices at the 95% C.L. for $\Lambda =1.5\mathrm{TeV}$. Limits on $S$-matrix unitarity are represented by the dotted lines.

Figure 8

The 2D (contour) and 1D (cross) limits on coupling parameters for (a) $ZZ\gamma$ and (b) $Z\gamma \gamma$ vertices at the 95% C.L. for $\Lambda =1.5\mathrm{TeV}$. Limits on $S$-matrix unitarity are represented by the dotted lines.