Observation of Same-Sign $WW$ Production from Double Parton Scattering in Proton-Proton Collisions at $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$

The first observation of the production of ${W}^{±}{W}^{±}$ bosons from double parton scattering processes using same-sign electron-muon and dimuon events in proton-proton collisions is reported. The data sample corresponds to an integrated luminosity of $138\text{}\text{}{\mathrm{fb}}^{-1}$ recorded at a center-of-mass energy of 13 TeV using the CMS detector at the CERN LHC. Multivariate discriminants are used to distinguish the signal process from the main backgrounds. A binned maximum likelihood fit is performed to extract the signal cross section. The measured cross section for production of same-sign $W$ bosons decaying leptonically is $80.7±11.2\left(\mathrm{stat}\right){\text{}}_{-8.6}^{+9.5}\left(\mathrm{syst}\right)±12.1\left(\mathrm{model}\right)\text{}\text{}\mathrm{fb}$, whereas the measured fiducial cross section is $6.28±0.81\left(\mathrm{stat}\right)±0.69\left(\mathrm{syst}\right)±0.37\left(\mathrm{model}\right)\text{}\text{}\mathrm{fb}$. The observed significance of the signal is 6.2 standard deviations above the background-only hypothesis.