Pentaquark states in a diquark–triquark model

The diquark–triquark model is used to explain charmonium-pentaquark states, i.e., Pc(4380)Pc(4380) and Pc(4450)Pc(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 52+ and 32− is around 100 MeV, which may naturally solve the challenging problem of small mass splitting between Pc(4450)Pc(4450) and Pc(4380)Pc(4380). This helps to understand the peculiarities of Pc(4380)Pc(4380) with a broad decay width whereas Pc(4450)Pc(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.