We calculate the invariant and helicity amplitudes for the transitions ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}^{(*)}(J^P)+J/\psi$, where the ${\mathrm{\Lambda }}^{(*)}(J^P)$ are $\mathrm{\Lambda }(sud)$-type ground and excited states with $J^P$ quantum numbers $J^P={\frac{1}{2}}^{\pm }$, ${\frac{3}{2}}^{\pm }$. The calculations are performed in the framework of a covariant confined quark model previously developed by us. We find that the values of the helicity amplitudes for the ${\mathrm{\Lambda }}^{*}(1520,{\frac{3}{2}}^{-})$ and the ${\mathrm{\Lambda }}^{*}(1890,{\frac{3}{2}}^{+})$ are suppressed compared with those for the ground state $\mathrm{\Lambda }(1116,{\frac{1}{2}}^{+})$ and the excited state ${\mathrm{\Lambda }}^{*}(1405,{\frac{1}{2}}^{-})$. This analysis is important for the identification of the hidden charm pentaquark states $P_c^{+}(4380)$ and $P_c^{+}(4450)$ which were discovered in the decay chain ${\mathrm{\Lambda }}_b^0\to P_c^{+}(\to pJ/\psi )+K^{-}$ because the cascade decay chain ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}^{*}({\frac{3}{2}}^{\pm })(\to p{K}^{-})+J/\psi$ involves the same final state.

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• Electroweak interaction
• Form factors
• Particle phenomena