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arXiv:2403.19343v1 Announce Type: new
Abstract: We study the elastic electric and magnetic form factors of the proton, neutron and the charged roper resonance ($G_E^p$, $G_M^p$, $G_E^n$, $G_M^n$, $G_E^R$ and $G_M^R$) systematically in a constituent quark model. Three ingredients are crucial in this study: i) the mixing of the $|70, ^{2}8,2,0,(\frac{1}{2})^{\textmd{+}}\rangle$ and the $|56, ^{2}8,0,0,(\frac{1}{2})^{\textmd{+}}\rangle$ which produces a nonzero neutron electric form factor. ii) a running coupling constant that soften the form factors. iii) the running quark mass function, $M_q(p^2)$, which is responsible for the decreasing of the $\mu_p G_E^p(Q^2)/G_M^p(Q^2)$ as $Q^2$ increases. The produced elastic form factors of the proton and neutron match the corresponding experiment values fairly well. Our study shows that $\mu_p G_E^p(Q^2)/G_M^p(Q^2) \approx M_q(Q^2/9)/M_q(0)$ upto $Q^2 \approx 4 \text{GeV}^2$. We give predictions on the elactic form factors of the roper resonance, the charge and magnetic radius of the roper resonance compared with proton are $r^R_{E}/r^p_{E} \approx r^R_{M}/r^p_{M} \approx 1.5$.