Molecular states from $\bar{B}^{(*)}N$ interactions

Abstract

In 2019, two new structures $\Lambda_b(6146)$ and $\Lambda_b(6152)$ were observed by the LHCb Collaboration at the invariant mass spectrum of $\Lambda_b^0\pi^{+}\pi^{-}$, which aroused a hot discussion about their inner structures. The $\Lambda_b(6146)$ and $\Lambda_b(6152)$ might still be molecular states because their masses are close to threshold of a $\bar{B}$ meson and a nucleon. In this work, we perform a systematical investigation of possible heavy baryonic molecular states from the $\bar{B}N$ interaction. Since the $\bar{B}N$ channel strongly couples to the $\bar{B}^{*}N$ channel, the possible $\bar{B}N-\bar{B}^{*}N$ bound states are also studied. The interaction of the system considered is described by the $t$-channel $\sigma$, $\pi$, $\eta$ ,$\omega$, and $\rho$ mesons exchanges. By solving the non-relativistic Schr\"{o}dinger equation with the obtained one-boson-exchange potentials, the $\bar{B}^{(*)}N$ bound states with different quantum numbers are searched. The calculation suggests that recently observed $\Lambda_b(6146)$ can be assigned as a $P$-wave $\bar{B}N$ molecular state with spin parity $J^P=3/2^{+}$ or a $\bar{B}N-\bar{B}^{*}N$ bound state. However, assignment of $\Lambda_b(6152)$ as an $F$-wave $\bar{B}N$ molecular is disfavored. The $\Lambda_b(6152)$ can be explained as meson-baryon molecular state with a small $\bar{B}N$ component. The calculation also predict the existence of two $S$-wave $\bar{B}N-\bar{B}^{*}N$ bound states that can be related to the experimentally observed $\Lambda_b(5912)$ and $\Lambda_b(5920)$.