Flavor-singlet hidden charm pentaquark

One type of hidden charm pentaquark P-cs with quark content c (c) over bar uds in light-flavor singlet state is studied in the quark model. This state is analogous to the P-c with c (c) over bar uds in light-flavor octet, which was observed in LHC in 2015. Considering various combinations of color, spin, and light flavor as internal quantum numbers in P-cs, we investigate the mass ordering of the P-cs's by adopting both the one-gluon exchange interaction and the instanton-induced interaction in the quark model. The most stable configuration of P-cs is identified to be total spin 1/2 in which the c (c) over bar uds is combined to be color octet and spin 1, while the uds cluster is in a color octet state. The other color octet configurations, the total spin 1/2 state with the c (c) over bar spin 0, and the state with total spin 3/2 and c (c) over bar spin 1, are found as excited states. We also discuss possible decay modes of these hidden charm pentaquarks.