Valence Quarks Polarization from COMPASS

A first evaluation of the polarized valence quark distribution $\Delta u_v(x)+\Delta d_v(x)$ from the COMPASS experiment (CERN/SPS) is presented. The data were collected by COMPASS in the years 2002–2004 using a 160 GeV polarized muon beam scattered off a large polarized ${}^6$LiD target and cover the range $1<Q^2<100$ GeV${}^2$ and $0.006<x<0.7$. The analysis is based on the difference asymmetry, $A^{h^{+}-h^{-}}$, for hadrons of opposite charges, which gives a direct access to the polarization of valence quarks.