Electroproduction of the Roper resonance as a hybrid state

We derive the ${\mathit{Q}}^2$ dependence of the helicity amplitudes of the Roper resonance assuming that it is (1) a radially excited ${\mathit{q}}^3$ state, and (2) a ${\mathit{q}}^3$G hybrid baryon. Our study shows that for a hybrid baryon assignment the magnitude of the transverse helicity amplitude decreases rapidly as ${\mathit{Q}}^2$ increases, and the longitudinal helicity amplitude vanishes. This behavior is quite different from the predictions of the ${\mathit{q}}^3$ quark potential model, which assumes a radially excited ${\mathit{q}}^3$ assignment. Comparison with data shows that the hybrid interpretation of the Roper resonance is favored. Future experiments at the Continuous Electron Beam Accelerator Facility should be able to clearly distinguish between these two possible assignments.