Fiducial and differential measurements of $W^{+}W^{-}$ production in decay topologies inspired by searches for electroweak supersymmetry in two-lepton final states

This note presents a measurement of fiducial and differential cross-sections for $W^{+}W^{-}$ production in proton-proton collisions at $\sqrt{s}=13$ TeV with the ATLAS experiment at the Large Hadron Collider using a dataset corresponding to an integrated luminosity of 139 fb$^{-1}$. Events with exactly one electron, one muon and no hadronic jets are studied. The fiducial region in which the measurements are performed is inspired by searches for the electroweak production of supersymmetric charginos decaying to two-lepton final states and is complementary to existing ATLAS measurements. Events are selected with moderate values of missing transverse momentum and the ``stransverse mass'' variable $m_{\mathrm{T2}}$, which is widely used in searches for supersymmetry at the LHC. The ranges of these variables are chosen to enhance direct $W^{+}W^{-}$ production and suppress production via top quarks, which is treated as a background. Particle-level differential cross-sections for six variables are compared to theoretical predictions, with good agreement observed for all observables.