The LHCb pentaquark as a $\bar{D}^*��_c-\bar{D}^*��_c^*$ molecular state

We perform a theoretical analysis of the $��_b \to J/��K^- p$ reaction from where a recent LHCb experiment extracts a $��(1405)$ contribution in the $K^- p$ spectrum close to threshold and two baryon states of hidden charm in the $J/��\,p$ 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 $J/��\, N$, $\bar D^* ��_c$, $\bar D^* ��_c$, $\bar D ��^*_c$ and $\bar D^* ��^*_c$ 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 $J/��\,p$ distribution, with values of the $J/��\, p$ coupling to the resonance in line with the theoretical ones. The non trivial 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 $\bar D^* ��_c$ and $\bar D^* ��^*_c$.
4 pages, 2 figures