Observation of electroweak W W Pair Production in Association With two Jets in Proton-proton Collisions at

An observation is reported of the electroweak production of a ${\text{W}}^{+}{\text{W}}^{-}$ pair in association with two jets, with both W bosons decaying leptonically. The data sample corresponds to an integrated luminosity of 138fb$^{−1}$ of proton-proton collisions at $\sqrt{s}=13\phantom{\rule{0.2em}{0ex}}\text{TeV}$, collected by the CMS detector at the CERN LHC. Events are selected by requiring exactly two opposite-sign leptons (electrons or muons) and two jets with large pseudorapidity separation and high dijet invariant mass. Events are categorized based on the flavor of the final-state leptons. A signal is observed with a significance of 5.6 standard deviations (5.2 expected) with respect to the background-only hypothesis. The measured fiducial cross section is $10.2±2.0\phantom{\rule{0.2em}{0ex}}\text{fb}$ and this value is consistent with the standard model prediction of $9.1±0.6\phantom{\rule{0.2em}{0ex}}\text{fb}$.