Measurement of the WW + WZ production cross section in a semileptonic decay mode at CDF

The measurement of the WW + WZ production cross section in a semileptonic decay mode is presented. The measurement is carried out with 4.6 fb-1 of integrated luminosity collected by the CDF II detector in s = 1.96 TeV proton-antiproton collisions at the Tevatron. The main experimental challenge is identifying the signal in the overwhelming background from W +jets production. The modeling of the W +jets background is carefully studied and a matrix element technique is used to build a discriminant to separate signal and background. The cross section of WW + WZ production is measured to be sigma( pp¯ → WW + WZ) = 16.5+3.3-3.0 pb, in agreement with the next-to-leading order theoretical prediction of 15.1 +/- 0.9 pb. The significance of the signal is evaluated to be 5.4sigma. This measurement is an important milestone in the search for the Standard Model Higgs boson at the Tevatron.