XVIII International Conference on Hadron Spectroscopy and Structure (HADRON2019)

The recent experiments by LHCb indicates that the $NJ/\psi$-$\Lambda_c \bar D$-$\Sigma_c \bar D$ or $q^3c\bar c$ systems have a rich spectrum [1]. Theoretically also, it has been found that a quark cluster model, or a hadron model which includes the five-quark mode, gives narrow resonances or cusps in the $Y_c \bar D$ scattering [2,3]. Such a structure appears because the three light quarks in the system can take a color-octet isospin-1/2 spin-3/2 configuration, in which the color-magnetic interaction becomes attractive comparing to the relevant threshold. Here we discuss the strange pentaquark systems with the hidden heavy quark pair. The three light quarks now can also form a color-octet flavor-singlet spin-1/2 configuration. Then, the color magnetic interaction is more attractive than the isospin-1/2 case and causes a baryon-meson bound state. We argue that the pentaquarks with strangeness can be candidates of the exotic baryons. [1] R.Aaij et al., [LHCb Collaboration], arXiv:1904.03947 [hep-ex]. [2] S.Takeuchi and M.Takizawa, Phys.Lett.B764, 254 (2017) [3] Y.Yamaguchi, A.Giachino, et.al., Phys.Rev.D96,114031 (2017)