Observation of electroweak Boson Pair Production in Association With two Jets in Collisions at TeV with the ATLAS detector

An observation of electroweak ${W}^{±}Z$ production in association with two jets in proton–proton collisions is presented. The data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of $\sqrt{s}=13$ TeV are used, corresponding to an integrated luminosity of $36.1\phantom{\rule{0.25em}{0ex}}{\text{fb}}^{-1}$. Events containing three identified leptons, either electrons or muons, and two jets are selected. The electroweak production of ${W}^{±}Z$ bosons in association with two jets is measured with an observed significance of 5.3 standard deviations. A fiducial cross-section for electroweak production including interference effects and for a single leptonic decay mode is measured to be ${\sigma }_{WZjj-\mathrm{EW}}=0.57\phantom{\rule{0.25em}{0ex}}{}_{-0.13}^{+0.14}\phantom{\rule{0.2em}{0ex}}\left(\mathrm{stat}.\right)\phantom{\rule{0.25em}{0ex}}{}_{-0.06}^{+0.07}\phantom{\rule{0.2em}{0ex}}\left(\mathrm{syst}.\right)\phantom{\rule{0.25em}{0ex}}\mathrm{fb}$. Total and differential fiducial cross-sections of the sum of ${W}^{±}Zjj$ electroweak and strong productions for several kinematic observables are also measured.