Negative parity pentaquarks in large $N_c$ QCD and quark model

Recently, the $1/N_c$ expansion has been applied to the study of exotic baryons containing both quarks and antiquarks. We extend this approach to exotic states with mixed-symmetric spin-flavor symmetry, which correspond in the quark model to negative parity pentaquarks, and discuss the large $N_c$ predictions for their mass spectrum. The heavy exotics $\overline{Q}{q}^4$ transform as $\mathbf{3},\overline{\mathbf{6}},\mathbf{15}$ and ${\mathbf{15}}^{\prime }$ under SU(3), while the light states $\overline{q}{q}^4$ include the exotic multiplets $\overline{\mathbf{10}},\mathbf{27},\mathbf{35}$. We give mass relations among these multiplets in the $1/N_c$ expansion. In the quark model, the mass splittings between these states are given by color-spin interactions. Using the observation of an anticharmed exotic by the H1 Collaboration, we give predictions for the masses of other expected heavy pentaquarks.

Figure 1

Weight diagrams for heavy pentaquarks with quark content $\overline{Q}{q}^4$.