The inclusive double-spin asymmetry, $A^p_1$, has been measured at COMPASS in deepinelastic polarised muon scattering off a large polarised NH3 target. The data, collected in the year 2007, cover the range $Q^2 > 1 (GeV/c)^2, 0.004 < x < 0.7$ and improve the statistical precision of $g^p_1(x)$ by a factor of two in the region $x < 0.02$. The new proton asymmetries are combined with those previously published for the deuteron to extract the non-singlet spin-dependent structure function $g^{NS}_1(x,Q^2)$. The isovector quark density, $\Delta_{q3}(x,Q^2)$, is evaluated from a NLO QCD fit of $g^{NS}_1$. The first moment of $\Delta_{q3}$ is in good agreement with the value predicted by the Bjorken sum rule and corresponds to a ratio of the axial and vector coupling constants $|g_A/g_V$ = $1.28\pm 0.07(stat)\pm 0.10$(syst).
Values of A1P and G1P as a function of X with corresponding average values of Q**2.
Values of $A_1^p$ and $g_1^p$ as a function of $x$ with corresponding average values of $Q^2$.
Values of $g_1^p$ for the 2007 COMPASS proton data at 160 GeV in ($x$, $Q^2$) bins.
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