Strange Sea Polarization in the Proton and a Constituent Quark Model

Abstract

The valence-quark and q q -sea polarizations in the polarized proton are calculated in the frame­ work of a constituent quark model. It is pointed out that the configuration mixing of the symmetric three-quark state with the quark-diquark state gives a good fit to existing data on the strange sea polarization in the proton. Recently, the Spin Muon Collaboration (SMC) reported on the measurement of the spin-dependent structure function of the deuteron 1 > and pointed out that its first moment is smaller than the prediction of the Ellis-Jaffe sum rule 2 > as already found by the European Muon Collaboration (EMC). 3 > Namely, they conclude that the quarks do not carry the spin of the nucleon and the strange sea polarization is large and negative. On the other hand, the SLAC group (E142) 4 > reported the opposite result from the measurement at Q 2 =2 GeV 2 , i.e., the guarks carry half the nucleon spin and the strange sea polarization is consistent with the one expected by the naive parton model. 2 > This apparent discrepancy is an open question. In this paper, we calculate the valence-quark and qq-sea polarizations in the polarized proton in the framework of a constituent quark model. 5 >,G> It is shown that the amount of the strange sea polarization is strongly dependent on the structure of constituents and the SUA3) symmetry breaking parameter in the qq sea polarization. It is pointed out that the configuration mixing of the simple three-quark state with the quark-diquark state gives a good fit to existing data on the strange sea polarization in the proton below Q 2 =12 GeV 2 • We allow a distinction between the valence and sea quarks in the proton with positive helicity. For the up- and down-quark polarizations, we write Llu=Lluv+ Llus and Lld=Lldv+Llds where Llu(Lld) denotes the polarization carried by the u quark (d quark). The subscripts V and S denote valence and sea, respectively. We introduce the valence-quark spin l:v(=Lluv+Lldv).7) We assume the isospin invariance of the sea-quark with respect to the up- and down-quark but the broken SUf(3) symmetry so that