Direct Measurement of theWProduction Charge Asymmetry inpp¯Collisions ats=1.96TeV

We present the first direct measurement of the $W$ production charge asymmetry as a function of the $W$ boson rapidity $y_W$ in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. We use a sample of $W\to e\nu$ events in data from $1{\mathrm{fb}}^{-1}$ of integrated luminosity collected using the CDF II detector. In the region $|y_W|<3.0$, this measurement is capable of constraining the ratio of up- and down-quark momentum distributions in the proton more directly than in previous measurements of the asymmetry that are functions of the charged-lepton pseudorapidity.