The ccbar Pentaquarks by a Quark Model

Abstract

Recent LHCb experiments have shown us that there are two resonances in the $J/\psi p$ channel in the ${\Lambda }_b$ decay, whose spin and parity are most probably (3/2${}^{-}$ 5/2${}^{+}$). In this work, we investigate the $I(J^P)=1/2(1/2^{-})$, $1/2(3/2^{-})$, and $1/2(5/2^{-})$ $uudc\bar{c}$ pentaquark states by employing the quark cluster model. It is found that the color-octet isospin-1/2 spin-3/2 $uud$ configuration gives an attraction to such five-quark systems. This configuration together with the color-octet $c\bar{c}$ pair gives structures around the ${\Sigma }_c^{(\ast )}\bar{D}{}^{(\ast )}$ thresholds: one bound state, two resonances, and one large cusp are found in the $uudc\bar{c}$ negative parity channels. We argue that these resonances and cusp may correspond to, or combine to form, the negative parity pentaquark peak observed by LHCb.

Comments: 4 pages, 4 figures, Proceedings of the 14th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU2016)