Study on the possible molecular states composed of $$\Lambda _c{\bar{D}}^*$$ , $$\Sigma _c{\bar{D}}^*$$ , $$\Xi _c{\bar{D}}^*$$ and $$\Xi _c'{\bar{D}}^
Hong-Wei Ke (School of Science, Tianjin University, Tianjin, 300072, China); Fang Lu (School of Science, Tianjin University, Tianjin, 300072, China); Hai Pang (School of Science, Tianjin University, Tianjin, 300072, China); Xiao-Hai Liu (School of Science, Tianjin University, Tianjin, 300072, China); Xue-Qian Li (School of Physics, Nankai University, Tianjin, 300071, China)
The measurements on a few pentaquarks states $$P_c(4440)$$ , $$P_c(4457)$$ and $$P_{cs}(4459)$$ excite our new interests about their structures. Since the masses of $$P_c(4440)$$ and $$P_c(4457)$$ are close to the threshold of $$\Sigma _c{\bar{D}}^*$$ , in the earlier works, they were regarded as molecular states of $$\Sigma _c{\bar{D}}^*$$ with quantum numbers $$I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$$ and $$\frac{1}{2}(\frac{3}{2}^-)$$ , respectively. In a similar way $$P_{cs}(4459)$$ is naturally considered as a $$\Xi _c{\bar{D}}^*$$ bound state with $$I=0$$ . Within the Bethe-Salpeter (B-S) framework we systematically study the possible bound states of $$\Lambda _c\bar{D}^*$$ , $$\Sigma _c{\bar{D}}^*$$ , $$\Xi _c{\bar{D}}^*$$ and $$\Xi _c'{\bar{D}}^*$$ . Our results indicate that $$\Sigma _c{\bar{D}}^*$$ can form a bound state with $$I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$$ , which corresponds to $$P_c(4440)$$ . However for the $$I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$$ system the attraction between $$\Sigma _c$$ and $${\bar{D}}^*$$ is too weak to constitute a molecule, so $$P_{c}(4457)$$ may not be a bound state of $$\Sigma _c{\bar{D}}^*$$ with $$I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$$ . As $$\Xi _c{\bar{D}}^*$$ and $$\Xi _c'{\bar{D}}^*$$ systems we take into account of the mixing between $$\Xi _c$$ and $$\Xi '_c$$ and the eigenstets should include two normal bound states $$\Xi _c{\bar{D}}^*$$ and $$\Xi _c'{\bar{D}}^*$$ with $$I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$$ and a loosely bound state $$\Xi _c{\bar{D}}^*$$ with $$I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$$ . The conclusion that two $$\Xi _c{\bar{D}}^*$$ bound states exist, supports the suggestion that the observed peak of $$P_{cs}(4459)$$ may hide two states $$P_{cs}(4455)$$ and $$P_{cs}(4468)$$ . Based on the computations we predict a bound state $$\Xi _c'{\bar{D}}^*$$ with $$I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$$ but not that with $$I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$$ . Further more accurate experiments will test our approach and results.