Search for anomalous quartic $WW\gamma \gamma$ couplings in dielectron and missing energy final states in $p\overline{p}$ collisions at $\sqrt{s}\mathbf{=}1.96\mathrm{TeV}$

We present a search for anomalous components of the quartic gauge boson coupling $WW\gamma \gamma$ in events with an electron, a positron and missing transverse energy. The analyzed data correspond to $9.7{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the D0 detector in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The presence of anomalous quartic gauge couplings would manifest itself as an excess of boosted $WW$ events. No such excess is found in the data, and we set the most stringent limits to date on the anomalous coupling parameters $a_0^W$ and $a_C^W$. When a form factor with ${\Lambda }_{\mathrm{cutoff}}=0.5\mathrm{TeV}$ is used, the observed upper limits at 95% C.L. are $|a_0^W/{\Lambda }^2|<0.0025{\mathrm{GeV}}^{-2}$ and $|a_C^W/{\Lambda }^2|<0.0092{\mathrm{GeV}}^{-2}$.

Figure 1

Diagrams contributing to $W$ boson pair production via photon exchange, with (a) triple $WW\gamma$ and (b) quartic $WW\gamma \gamma$ couplings.

Figure 2

The (a) leading electron $p_T$ at the preselection level, (b) the transverse mass of the ${\mathrm{E̸}}_T$ and the two electrons after the final selection, and (c) the output of the final BDT discriminant after the final selection. In (a) and (b), the last bin includes all events above the upper bound of the histogram. The hatched bands show the total systematic uncertainty on the background prediction, and the signal distributions are those expected for $a_0^W/{\Lambda }^2=5\times {10}^{-4}{\mathrm{GeV}}^{-2}$ and no form factor.

Figure 3

Two-parameter 68% and 95% C.L. limits with different assumptions about the signal: (a) no form factor, or a form factor with (b) ${\Lambda }_{\mathrm{cutoff}}=1$ or (c) 0.5 TeV.