Isomultiplet mass differences of ${(1/2\mathrm{}}^{+}$ and ${(3/2\mathrm{}}^{+}$ baryons are studied in the constituent-quark model. We find that the mass differences of octet and decuplet baryons can be explained well in the presence of photon-cloud contributions. In the charmed sector, only the ${\Sigma }_c^0$-${\Sigma }_c^{++}$ mass difference has recently been measured. By including the photon-cloud effects, we obtain a negative sign of the ${\Sigma }_c^0$-${\Sigma }_c^{++}$ mass difference.

• Received 20 April 1988

DOI:https://doi.org/10.1103/PhysRevD.38.1623