We perform a theoretical analysis of the ${\mathrm{\Lambda }}_b\to J/\psi K^{-}p$ reaction from where a recent LHCb experiment extracts a $\mathrm{\Lambda }(1405)$ contribution in the $K^{-}p$ spectrum close to threshold and two baryon states of hidden charm in the $J/\psi p$ spectrum. We recall that baryon states of this type have been theoretically predicted matching the mass, width and $J^P$ of the experiment; concretely some states built up from the $J/\psi N$, ${\overline{D}}^{*}{\mathrm{\Lambda }}_c$, ${\overline{D}}^{*}{\mathrm{\Sigma }}_c$, $\overline{D}{\mathrm{\Sigma }}_c^{*}$ and ${\overline{D}}^{*}{\mathrm{\Sigma }}_c^{*}$ coupled channels. We assume that the observed narrow state around 4450 MeV has this nature and we are able to describe simultaneously the shapes and relative strength of the the $K^{-}p$ mass distribution close to threshold and the peak of the $J/\psi p$ distribution, with values of the $J/\psi p$ coupling to the resonance in line with the theoretical ones. The nontrivial matching of many properties gives support to a $J^P=3/2^{-}$ assignment to this state and to its nature as a molecular state mostly made of ${\overline{D}}^{*}{\mathrm{\Sigma }}_c$ and ${\overline{D}}^{*}{\mathrm{\Sigma }}_c^{*}$.

• Received 21 July 2015

DOI:https://doi.org/10.1103/PhysRevD.92.094003