Evidence for Electroweak Production of $W^{\pm }{W}^{\pm }jj$ in $pp$ Collisions at $\sqrt{s}=8\mathrm{TeV}$ with the ATLAS Detector

This Letter presents the first study of $W^{\pm }{W}^{\pm }jj$, same-electric-charge diboson production in association with two jets, using $20.3{\mathrm{fb}}^{-1}$ of proton-proton collision data at $\sqrt{s}=8\mathrm{TeV}$ recorded by the ATLAS detector at the Large Hadron Collider. Events with two reconstructed same-charge leptons ($e^{\pm }{e}^{\pm }$, $e^{\pm }{\mu }^{\pm }$, and ${\mu }^{\pm }{\mu }^{\pm }$) and two or more jets are analyzed. Production cross sections are measured in two fiducial regions, with different sensitivities to the electroweak and strong production mechanisms. First evidence for $W^{\pm }{W}^{\pm }jj$ production and electroweak-only $W^{\pm }{W}^{\pm }jj$ production is observed with a significance of 4.5 and 3.6 standard deviations, respectively. The measured production cross sections are in agreement with standard model predictions. Limits at 95% confidence level are set on anomalous quartic gauge couplings.

Figure 1

The $m_{jj}$ distribution for events passing the inclusive region selections except for the $m_{jj}$ selection indicated by the dashed line. The black hatched band in the upper plot represents the systematic uncertainty on the total prediction. On the lower plot the shaded band represents the fractional uncertainty of the total background while the solid line and hatched band represents the ratio of the total prediction to background only and its uncertainty. The $W^{\pm }{W}^{\pm }jj$ prediction is normalized to the SM expectation.

Figure 2

The $|\mathrm{\Delta }{y}_{jj}|$ distribution for events passing all inclusive region selections. The $|\mathrm{\Delta }{y}_{jj}|$ selection is indicated by a dashed line. The $W^{\pm }{W}^{\pm }jj$ prediction is normalized to the SM expectation.

Figure 3

Limits on (${\alpha }_4$,${\alpha }_5$). Points outside of the solid light ellipse are excluded by the data at 95% confidence level (C.L.). Points outside the inner dark ellipse are excluded at the 68% confidence level. The expected exclusion is given by the solid line.