We investigate the resonant baryonic $B$ decay $B^-\to { \cal P}_{ cs}^0\bar p,{ \cal P}_{ cs}^0\to J/\psi \Lambda$, where ${ \cal P}_{ cs}^0\equiv { \cal P}_{ cs}(4338)^0$ is identified as a hidden charm pentaquark candidate with strangeness. By interpreting ${ \cal P}_{ cs}^0$ as the $\Xi_c\bar D$ molecule that strongly decays into $J/\psi\Lambda$ and $\eta_c\Lambda$, we discover a dominant triangle rescattering effect for $B^-\to { \cal P}_{ cs}^0\bar p$, initiated by $B^-\to J/\psi K^-$. Through the exchange of a $\bar \Lambda$ anti-baryon, $J/\psi$ and $K^-$ undergo rescattering, transforming into ${ \cal P}_{ cs}^0$ and $\bar p$, respectively. Based on this rescattering mechanism, we calculate ${ \cal B}(B^-\to { \cal P}_{ cs}^0\bar p,{ \cal P}_{ cs}^0\to J/\psi \Lambda) =(1.4^{ +2.1}_{ -1.1})\times10^{ -6}$, which is consistent with the measured data.
Categories: hep-ph hep-ex