Friday, June 14, 2013

1306.3041 (C. S. An et al.)

Strangeness magnetic form factor of the proton in the extended chiral
quark model

C. S. An, B. Saghai
{\bf Background:} Unravelling the role played by nonvalence flavors in baryons is crucial in deepening our comprehension of QCD. Strange quark, a component of the higher Fock states in baryons, is an appropriate tool to investigate nonperturbative mechanisms generated by the pure sea quark. {\bf Purpose:} Study the magnitude and the sign of the strangeness magnetic moment $\mu_s$ and the magnetic form factor ($G_M^s$) of the proton. {\bf Methods:} Within an extended chiral constituent quark model, we investigate contributions from all possible five-quark components to $\mu_s$ and $G_M^s (Q^2)$ in the four-vector momentum range $Q^2 \leq 1$ (GeV/c)$^2$. Probability of the strangeness component in the proton wave function is calculated employing the $^3 P_0$ model. {\bf Results:} Predictions are obtained without any adjustable parameters. Observables $\mu_s$ and $G_M^s (Q^2)$ are found to be small and negative, consistent with the lattice-QCD findings as well as with the latest data released by the PVA4 and HAPPEX Collaborations. {\bf Conclusions:} Due to sizeable cancelations among different configurations contributing to the strangeness magnetic moment of the proton, it is indispensable to {\it i)} take into account all relevant five-quark components and include both diagonal and non-diagonal terms, {\it ii)} handle with care the oscillator harmonic parameter $\omega_5$ and the ${s \bar s}$ component probability.
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