Pentaquark states in a diquark-triquark model

TL;DR

This paper uses a diquark-triquark model to explain observed pentaquark states, introducing a nonlocal distribution amplitude and an effective Hamiltonian to account for mass splittings and decay widths, and predicts additional states.

Contribution

It is the first to investigate the properties of a nonlocal diquark-triquark configuration and establish an effective Hamiltonian for pentaquark states, explaining mass splittings and decay behaviors.

Findings

Mass splitting between states is around 100 MeV.

Pentaquark states P_c(4380) and P_c(4450) have different decay widths.

Model predicts additional pentaquark states for future experiments.

Abstract

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 $\frac{5}{2}^+$ and $\frac{3}{2}^-$ 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.