Polarised quark distributions in the nucleon from semi-inclusive spin asymmetries

We present a measurement of semi-inclusive spin asymmetries for positively and negatively charged hadrons from deep inelastic scattering of polarised muons on polarised protons and deuterons in the range 0.003<x<0.7 and Q2>1 GeV2. Compared to our previous publication on this subject, with the new data the statistical errors have been reduced by nearly a factor of two. From these asymmetries and our inclusive spin asymmetries we determine the polarised quark distributions of valence quarks and non-strange sea quarks at Q2=10 GeV2. The polarised u valence quark distribution, Δuv(x), is positive and the polarisation increases with x. The polarised d valence quark distribution, Δdv(x), is negative and the non-strange sea distribution, Δq̄(x), is consistent with zero over the measured range of x. We find for the first moments ∫01Δuv(x)dx=0.77±0.10±0.08, ∫01Δdv(x)dx=−0.52±0.14±0.09 and ∫01Δq̄(x)dx=0.01±0.04±0.03, where we assumed Δū(x)=Δd̄(x). We also determine for the first time the second moments of the valence distributions ∫01xΔqv(x)dx.