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We present the first direct measurement of the W production charge asymmetry as a function of the W boson rapidity yW in pp̄ collisions at s=1.96TeV. We use a sample of W→eν events in data from 1fb-1 of integrated luminosity collected using the CDF II detector. In the region |yW|<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. © 2009 The American Physical Society.

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Physical Review Letters