Polarizations of Sea and Gluon in the Proton and Valence Quark Spins

Abstract

Recently, the European Muon Collaboration (EMC) measured the polarized structure function of the proton g/(x, Q2).1) The EMC found that the value of the first moment of g/(x, Q2) is smaller than the one expected by the naive quark modeL) The result has been investigated by means of various approaches. However, the sign. and magnitude of the sea and gluon polarizations are not clear. For example, Kobayakawa et aL) suggest the positive sea and positive gluon polarizations, while Cheng et aL) do the negative sea and negative gluon polarizations. Also, many authors),6) have discussed the negative sea and positive gluon polarizations. It is important to clarify the relations among their results. In this paper, we investigate the sea and gluon polarizations in the proton by considering the effect of the anomaly7) and the broken flavour-SU(3) (SUA3)) sea. It is pointed out that the sign and magnitude of the sea and gluon contributions demanded by the experimental data, are strongly correlated to the amount of the spins carried by valence quarks and the SUA3) symmetry breaking parametenwhen combined with the data of neutron and hyperon beta decays.S),9) Also, we calculate the magnitude of the valence quark spins in a framework of a constituent quark model,6) as an example. We consider the polarized parton distributions in a proton with positive helicity. Let us introduce the helicity-weighted quark and gluon densities Llq(x, Q2), Llg(x, Q2) and their polarizations (first moments) Llq( Q2), Llg( Q2) at Q2 Ge V: