YSF Observation of VBS production in opposite-sign WW events at CMS

The first observation of Vector Boson Scattering (VBS) in the W$^{+}$W$^{-}$ channel is presented. The analyzed data sample corresponds to an integrated luminosity of 138 \ensuremath{\mathrm{fb^{-1}}} of proton-proton collisions at $\sqrt{s} = 13$ TeV, collected by the CMS detector at the CERN LHC. Fully leptonic final states have been considered, selecting events with exactly two opposite-sign leptons (either electrons or muons) and missing transverse energy due to the escaping neutrinos. Additionally, at least two jets with large pseudorapidity gap (\ensuremath{\Delta\eta_{\mathrm{jj}}}) and high invariant mass (\ensuremath{m_{\mathrm{jj}}}) are required, which are produced in association with the two W bosons. 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 $10.2 \pm 2.0$ fb and is consistent with the standard model (SM) prediction ($9.1 \pm 0.6$ fb).