Evidence for WW production from double-parton interactions in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A study of WW production from double-parton scattering processes using same-charge dimuon and electron-muon events is carried out based on proton-proton collision data at a center-of-mass energy of 13 TeV. The analyzed data set corresponds to an integrated luminosity of 77 fb$^{-1}$, collected with the CMS detector during 2016 and 2017 at the CERN LHC. Multivariate classifiers are used to discriminate between the signal and the dominant background processes. A maximum likelihood fit is performed to extract the signal cross section. The observed significance of the double-parton scattering WW process is 3.9 standard deviations, and the measured inclusive cross section is 1.41 $\pm$ 0.28 (stat) $\pm$ 0.28 (syst) pb.