Novel Pentaquarks from Diquark-Triquark Model

We use constituent diquark-triquark model to explain the charmonium-pentaquark states, i.e. $P_c(4380)$ and $P_c(4450)$ which have been recently discovered by the LHCb collaboration. We analyze the color attractive configuration for the triquark and define the nonlocal wave functions for the pentaquark state for the first time, where both diquark and triquark are not a compact pointlike, but have a nonzero size. An effective diquark-triquark Hamiltonian based on spin-orbital interaction is established. One then obtain the minimum orbital excitation mass splitting between $\frac{5}{2}^+$ and $\frac{3}{2}^-$ can be near $100$MeV, which naturally clarifies the challenging issue, i.e. the small mass splitting between $P_c(4450)$ and $P_c(4380)$. The issue that broad decay width of $P_c(4380)$ and narrow decay width of $P_c(4450)$ can also be understood in this model. The predicted novel pentaquarks can be tested from experiment, which can inspect the diquark-triquark model conversely.