Pentaquark states in a diquark-triquark model

The diquark-triquark model is used to explain charmonium-pentaquark states, i.e., P-c(4380) and P-c(4450), which were observed recently by the LHCb Collaboration. For the first time, we investigate the properties of the color attractive configuration of a triquark and we define a nonlocal light cone distribution amplitude for pentaquark states, where both diquark and triquark are not pointlike, but they have nonzero size. We establish an effective diquark-triquark Hamiltonian based on spin-orbital interaction. According to the Hamiltonian, we show that the minimum mass splitting between 5/2(+) and 3/2(-) is around 100 MeV, which may naturally solve the challenging problem of small mass splitting between P-c(4450) and P-c(4380). This helps to understand the peculiarities of P-c(4380) with a broad decay width whereas P-c(4450) has a narrow decay width. Based on the diquark-triquark model, we predict more pentaquark states, which will hopefully be measured in future experiments. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license.