Nucleonic Properties in Statistical Model

Abstract

Nucleon is considered as a statistical system, and a nucleon state is expanded in terms of quark and gluon Fock states. In the present thesis, we have used the model approach to study various low-energy properties of a nucleon appropriate for the method concerned. The composition of nucleons in terms of fundamental quark and gluon degrees of freedom has been modeled variously to account for their observed properties. We work in a statistical model in which a nucleon is taken as an ensemble of quark-gluon Fock states. A spin up nucleon state has been expanded in Fock states consisting of three valence quarks and a sea consisting of quarks, antiquarks and gluons, and containing up to five constituents which have definite spin and color quantum numbers. The expansion of a Fock state into spin and color states has been done using the assumption of equal probability for each substate of such a state. We also use the approximation in which a quark in the core is not antisymmetrized with an identical quark in the sea, and have treated quarks and gluons as non-relativistic particles moving in S-wave motion. We have not taken into account any contribution of s-quark and other heavy quarks, and have covered only ~ 85% of the total Fock states. The remaining Fock states have been assumed to be decomposed in approximately same proportion as the earlier discussed case. With these approximations, we have calculated the quark contribution to the spin of the nucleons, the ratio of the magnetic moments of the nucleons, their weak decay constant. Our values makes better agreement with the data .