Chiral quark model and the nucleon spin

Abstract

Using \chiQM with configuration mixing, the contribution of the gluon polarization to the flavor singlet component of the total spin has been calculated phenomenologically through the relation \Delta\Sigma(Q^2)=\Delta\Sigma-\frac{3\alpha_s(Q^2)}{2\pi}\Delta g(Q^2) as defined in the Adler-Bardeen scheme, where \Delta\Sigma on the right hand side is Q^2 independent. For evaluation the contribution of gluon polarization \Delta g'(=\frac{3\alpha_s(Q^2)}{2\pi}\Delta g(Q^2)), \Delta\Sigma is found in the \chiQM by fixing the latest E866 data pertaining to \bar u-\bar d asymmetry and the spin polarization functions whereas \Delta \Sigma(Q^2) is taken to be 0.30\pm0.06 and \alpha_s= 0.287\pm0.020, both at Q^2=5{\rm GeV}^2. The contribution of gluon polarization \Delta g' comes out to be 0.33 which leads to an almost perfect fit for spin distribution functions in the \chiQM. When its implications for magnetic moments are investigated, we find perfect fit for many of the magnetic moments. If an attempt is made to explain the angular momentum sum rule for proton by using the above value of \Delta g', one finds the contribution of gluon angular momentum to be as important as that of the q \bar q pairs.