The polarised valence quark distribution from semi-inclusive DIS
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The semi-inclusive difference asymmetry Ah+ - h- for hadrons of opposite charge has been measured by the COMPASS experiment at CERN. The data were collected in the years 2002-2004 using a 160 GeV polarised muon beam scattered off a large polarised 6LiD target in the kinematic range 0.006 < x < 0.7 and 1 < Q2 < 100 (GeV / c)2. In leading order QCD (LO) the deuteron asymmetry Ah+ - h- measures the valence quark polarisation and provides an evaluation of the first moment of Δ uv + Δ dv which is found to be equal to 0.40 ± 0.07 (stat.) ± 0.06 (syst.) over the measured range of x at Q2 = 10 (GeV / c)2. When combined with the first moment of g1d previously measured on the same data, this result favours a non-symmetric polarisation of light quarks Δ over(u, ̄) = - Δ over(d, ̄) at a confidence level of two standard deviations, in contrast to the often assumed symmetric scenario Δ over(u, ̄) = Δ over(d, ̄) = Δ over(s, ̄) = Δ s. © 2008 Elsevier B.V. All rights reserved.
author list (cited authors)
Collaboration, C., Alekseev, M., Alexakhin, V. Y., Alexandrov, Y. u., Alexeev, G. D., Amoroso, A., ... Zvyagin, A.