Rotational bands in the baryon spectrum

Abstract

As suggested by the bag model, we assume that the ground states of the nucleon and the $\Delta$ are nearly spherical, but the excited even-parity states are quite deformed. This deformation is responsible for the observed low-lying excitations $N\left(1440\right)\mathrm{}{\frac{1}{2}}^{+}$ and $\Delta \mathrm{}\left(1600\right)\mathrm{}{\frac{3}{2}}^{+}$, on which rotational bands are built.