Valence quark and meson cloud contributions to the $\gamma^\ast N \to N^\ast(1520)$ form factors

Abstract

The covariant spectator quark model is applied to the $\gamma^\ast N \to N^\ast(1520)$ reaction. The valence quark contributions to the electromagnetic form factors and helicity transition amplitudes are estimated from the covariant structure of the $N^\ast(1520)$ wave function calibrated by the experimental data for large squared momentum transfer $Q^2$. The difference between the model results and the experimental data is then used to parameterize the low $Q^2$ behavior, where meson cloud effects are assumed to dominate. This parametrization can be very useful for future studies of the reaction, as well as for the extension of the transition form factors to the timelike region.