CCAST, World Lab, Beijing 100080, Peoples R China
; Acad Sinica, Inst High Energy Phys, Beijing 100039, Peoples R China
; Univ Tecn Federico Santa Maria, Dept Fis, Valparaiso, Chile
; CNRS, Ctr Phys Theor, F-13288 Marseille, France
The quark helicity measured in polarized deep inelastic scattering is different from the quark spin in the rest frame of the nucleon. We point out that the quark spin distributions Delta q(RF)(x) are connected with the quark helicity distributions dq(x) and the quark transversity distributions delta q(x) by an approximate relation: Delta q(RF)(x) + Delta q(x) = 2 delta q(x). This relation will be useful in order to measure the rest frame (or quark model) spin distributions of the nucleon once the quark helicity distributions and quark transversity distributions are themselves measured. We also calculate the x-dependent quark transversity distributions delta q(x) and quark spin distributions Delta q(RF)(x) in a light-cone SU(6) quark-spectator model, and present discussions on possible effect from the sea quark-antiquark pairs. (C) 1998 Elsevier Science B.V. All rights reserved.