Molecular states from ${\bar{B}}^{(\ast )}N$ 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 ${\bar{B}}^{\ast }N$ channel, the possible $\bar{B}N-{\bar{B}}^{\ast }N$ 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 Schrödinger equation with the obtained one-boson-exchange potentials, the ${\bar{B}}^{(\ast )}N$ 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 $\bar{B}N-{\bar{B}}^{\ast }N$ 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 $\bar{B}N-{\bar{B}}^{\ast }N$ bound states that can be related to the experimentally observed ${\Lambda }_b(5912)$ and ${\Lambda }_b(5920)$.