Observation of electroweak production of $W^+W^-$ in association with jets using the ATLAS Detector

A measurement of the production of W bosons with opposite electric charges in association with two jets is presented based on $140\,\mathrm{fb}^{-1}$ of data collected by the ATLAS detector in proton-proton collisions at $\sqrt{s}=13\,\mathrm{TeV}$, during LHC Run 2. The analysis is sensitive to the scattering of W bosons, which is of particular interest in the ATLAS physics programme as it can be used to probe the electroweak symmetry breaking mechanism of the Standard Model. This signal has been observed for the first time in the ATLAS experiment with a significance of $7.1$ standard deviations, while $6.2$ were expected from the rejection of the background-only hypothesis. The observed cross section has been determined in a signal-enriched fiducial volume and is found to be $2.65^{+0.52}_{-0.48}\,\mathrm{fb}$, while the theoretical prediction from POWHEG is $2.20^{+0.14}_{-0.13}\,\mathrm{fb}$.