Measurement of the $t\bar{t}W$ and $t\bar{t}Z$ production cross sections in $pp$ collisions at $\sqrt{s} = 8 \mathrm{\ Te\kern -0.1em V}$ with the ATLAS detector

Understand

The production cross sections of top-quark pairs in association with massive vector bosons have been measured using data from $pp$ collisions at $\sqrt{s} = 8 \mathrm{\ Te\kern -0.1em V}$.

• The dataset corresponds to an integrated luminosity of $20.3\ \mathrm{fb}^{-1}$ collected by the ATLAS detector in 2012 at the LHC.
• Final states with two, three or four leptons are considered.
• A fit to the data considering the $t\bar{t}W$ and $t\bar{t}Z$ processes simultaneously yields a significance of $5.0\sigma$ ($4.2\sigma$) over the background-only hypothesis for $t\bar{t}W$ ($t\bar{t}Z$) production.