Structure of pentaquarks $P_c^{+}$ in the chiral quark model

The recent experimental results of the LHCb Collaboration suggested the existence of pentaquark states with a charmonium. To understand the structure of the states, a dynamical calculation of 5-quark systems with quantum numbers $I{J}^P=\frac{1}{2}(\frac{1}{2}{)}^{\pm }$, $\frac{1}{2}(\frac{3}{2}{)}^{\pm }$ and $\frac{1}{2}(\frac{5}{2}{)}^{\pm }$ is performed in the framework of the chiral quark model with the help of the Gaussian expansion method. The results show that there are several negative parity resonance states while all of the positive parity states are the scattering states. The $P_c(4380)$ state is suggested to be the pentaquark state of ${\mathrm{\Sigma }}_c^{*}\overline{D}$. Although the energy of ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ is very close to the mass of $P_c(4450)$, the inconsistent parity prevents the assignment. The calculated distances between quarks confirm the molecular nature of the states.

Figure 1

The binding energy of states with $I{J}^P=\frac{1}{2}{\frac{3}{2}}^{+}$ and $\frac{1}{2}{\frac{5}{2}}^{+}$ as a function of the mass of a $\sigma$ meson and cutoff ${\mathrm{\Lambda }}_{\sigma }$.