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. From these asymmetries and the previously published inclusive spin asymmetries we determine, for the first time, the x-dependent spin distributions for up and down valence quarks and for non-strange sea quarks. We find that the first moments of the valence quark spin distributions are Δuv = 1.01 ± 0.19 ± 0.14 and Δdv = -0.57 ± 0.22 ± 0.11. The spin distribution function of non-strange sea quarks is consistent with zero over the measured range of x and the first moment is Δū = Δd̄ = -0.02 ± 0.09 ± 0.03.
Adeva, B., Arik, E., Arvidson, A., Badelek, B., Ballintijn, M. K., Bardin, G., … Zhao, J. (1996). Polarisation of valence and non-strange sea quarks in the nucleon from semi-inclusive spin asymmetries. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 369(1), 93–100. https://doi.org/10.1016/0370-2693(95)01584-1