Compact hidden charm pentaquark states and QCD isomers

Abstract

We make an exhaustive investigation on the pentaquark states $qqqc\bar{c}$ ($q=u,d$ and $s$) and discuss the effect of color structures in a multiquark color flux-tube model. We exhibit a novel picture of the structure and properties of the states $P_c$ and $P_{cs}$ observed by the LHCb Collaboration. We can describe the states as the compact pentaquark states in the model. The spin-parity of the group of $P_c(4312{)}^{+}$ and $P_c(4337{)}^{+}$ is ${\frac{1}{2}}^{-}$ while that of the group of $P_c(4380{)}^{+}$, $P_c(4440{)}^{+}$ and $P_c(4457{)}^{+}$ is ${\frac{3}{2}}^{-}$. Their structures are pentagon, diquark, pentagon, diquark, and octet, respectively. The members in each group can be analogically called QCD isomers because of their the same spin-parity and quark content but different color structures. The singlet $P_{cs}(4459{)}^0$ has pentagon structure and spin-parity of ${\frac{1}{2}}^{-}$. In addition, we also predict the $P_{cs}$, $P_{css}$ and $P_{csss}$ families in the model. The five-body confinement potential based on the color flux-tube picture, which is a collective degree of freedom and induces QCD isomer phenomenon, plays an important role in the formation of the compact states.

Comments: 10 pages, 2 figures, 6 tables, comments are welcome