Up and down quark structure of the proton

We report an improved measurement of the valence and quark distributions from the forward-backward asymmetry in the Drell-Yan process using of data collected with the D0 detector in collisions at . This analysis provides the values of new structure parameters that are directly related to the valence up and down quark distributions in the proton. In other experimental results measuring the quark content of the proton, quark contributions are mixed with those from other quark flavors. In this measurement, the and quark contributions are separately extracted by applying a factorization of the QCD and electroweak portions of the forward-backward asymmetry.