The hidden charm pentaquarks are the hidden color-octet $uud$ baryons?

Abstract

The $I(J^P)=\frac{1}{2}({\frac{1}{2}}^{-})$, $\frac{1}{2}({\frac{3}{2}}^{-})$, and $\frac{1}{2}({\frac{5}{2}}^{-})$ $uudc\overline{c}$ pentaquarks are investigated by the quark cluster model. This model, which reproduces the mass spectra of the color-singlet $S$-wave $q^3$ baryons and $q\overline{q}$ mesons, also enables us to evaluate the quark interaction in the color-octet $uud$ configurations. It is shown that the color-octet isospin-$\frac{1}{2}$ spin-$\frac{3}{2}$ $uud$ configuration gains attraction. The $uudc\overline{c}$ states with this configuration have structures around the ${\Sigma }_c{}^{(\ast )}\overline{D}{}^{(\ast )}$ thresholds: one bound state, two resonances, and one large cusp are found. We argue that the negative parity pentaquark found by the LHCb experiments may be given by these structures.

Comments: 6 pages 4 figures, to be published in Physics Letters B