Direct Measurement of the W Production Charge Asymmetry in pp Collisions at root s=1.96 TeV

We present the first direct measurement of the W production charge asymmetry as a function of the W boson rapidity y(W) in pp collisions at root s=1.96 TeV. We use a sample of W -> e nu events in data from 1 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.