Rest Frame Properties of the Proton

Abstract

The proton is modeled as three quarks of smallcurrent quark mass. The threebody Dirac equation issolved with spin-independent central diagonal linearconfining potentials with an attractive Coulombic term in a relativistic threequark model.Hyperspherical coordinates are used, and the bound stateis found analytically. After integrating over thehyperangles, the Hamiltonian is an 8 by 8 matrix ofcoupled first-order differential equations in onevariable, the hyperradius. These are analytically solvedin hypercentral approximation. For the(1/2+)3 ground-state configurationin the nonrelativistic large-quark-mass limit, there are no nodes in the wave function.However, in the extreme relativistic limit of smallcurrent quark masses of a few MeV, the expectation valueof the number of nodes is about 1.30 when the potential parameters are chosen to reproducethe proton rms charge radius. The quarks are assumed topossess a Pauli anomalous magnetic moment, like that ofthe electron and muon of (α/2π)(e/m). Assuming all three quarks have equal mass, one can fitthe rest energy, magnetic moment, rms charge radius, andaxial charge of the proton with this relativisticthree-body Dirac equation model. The solution found shows the necessity of including all componentsof the composite three-quark wave function, as the uppercomponent contributes only 0.585 to the norm.