Polarized Sea Measurements at Jparc

Helicity distributions of valence quarks have been investigated in many experiments and are now well known. On the other hand, the distributions of the polarized sea are poorly known. In particular, concerning ∆ū(x), fits assuming a totally flavour symmetric sea suggest a sign opposite respect to fits based on a flavour broken sea . The situation is even more confused concerning the transversity polarized sea. While the estimate of the numerical value of δu(x) is more or less similar in all model calculations (the discrepancy is a factor 2 roughly), the uncertainties in the theoretical predictions for δū(x) are much more significant. Actually, there are essentially only two model calculations, one based on the Chiral Color-Dielectric Model (CCDM) 2 and one on the socalled Chiral Quark-Soliton Model (CQSM) . The two predictions differ not only on the size of the polarized sea, but also on the sign. While an experiment based on Drell-Yan production in pp scattering could only extract with large error bars the transversity polarized quark distributions, the sign of the asymmetry could be determined without any ambiguity, as long as the valence region is tested (xB > 0.1). An experiment at √ s ∼ 10 GeV as foreseen at JPARC can explore this region.