Measurement of the WW Production Cross Section in pp̅ Collisions at √ s = 1.96 TeV

We present a measurement of the W boson pair-production cross section in pp collisions at a center-of-mass energy of √s=1.96 TeV. The data, collected with the Run II D0 detector at Fermilab, correspond to an integrated luminosity of 224-252 pb -1 depending on the final state (ee, eμ, or μμ). We observe 25 candidates with a background expectation of 8.1±0.6(stat)±0.6(syst)±0.5(lum) events. The probability for an upward fluctuation of the background to produce the observed signal is 2.3x10 -7 , equivalent to 5.2 standard deviations. The measurement yields a cross section of 13.8 -3.8 +4.3 (stat) -0.9 +1.2 (syst)±0.9(lum) pb, in agreement with predictions from the standard model.