Observation of Diboson Production in a Semileptonic Decay at CDF

We present the first observation of WW+WZ production in the channel with an identified lepton and two jets in 2.7 fb${}^{-1}$ of integrated luminosity collected with the CDF II detector in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV. The signal is separated from the large background using matrix element calculations and is observed with a significance of 5.4$\sigma$. The WW+WZ production cross section is measured to be $17.7\pm 3.1$(stat)$\pm 2.4$(sys) pb, in good agreement with standard model predictions. A complimentary measurement using a fit to the dijet mass is also presented.