Measurement of theWWProduction Cross Section inpp¯Collisions ats=1.96TeV

We present a measurement of the $W$ boson pair-production cross section in $p\overline{p}$ collisions at a center-of-mass energy of $\sqrt{s}=1.96\mathrm{TeV}$. The data, collected with the Run II D0 detector at Fermilab, correspond to an integrated luminosity of $224–252{\mathrm{pb}}^{-1}$ depending on the final state ($ee$, $e\mu$, or $\mu \mu$). We observe 25 candidates with a background expectation of $8.1\pm 0.6(\mathrm{stat})\pm 0.6(\mathrm{syst})\pm 0.5(\mathrm{lum})$ events. The probability for an upward fluctuation of the background to produce the observed signal is $2.3\times {10}^{-7}$, equivalent to 5.2 standard deviations. The measurement yields a cross section of ${13.8}_{-3.8}^{+4.3}(\mathrm{stat}{)}_{-0.9}^{+1.2}(\mathrm{syst})\pm 0.9(\mathrm{lum})\mathrm{pb}$, in agreement with predictions from the standard model.