LHCb pentaquark as a D ¯ ∗ Σc- D ¯ ∗ Σc∗ molecular state

Abstract

We perform a theoretical analysis of the Λb→J/ψK-p reaction from where a recent LHCb experiment extracts a Λ(1405) contribution in the K-p spectrum close to threshold and two baryon states of hidden charm in the J/ψp spectrum. We recall that baryon states of this type have been theoretically predicted matching the mass, width and JP of the experiment; concretely some states built up from the J/ψN, D¯∗Λc, D¯∗Σc, D¯Σc∗ and D¯∗Σc∗ 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/ψp distribution, with values of the J/ψp coupling to the resonance in line with the theoretical ones. The nontrivial matching of many properties gives support to a JP=3/2- assignment to this state and to its nature as a molecular state mostly made of D¯∗Σc and D¯∗Σc∗.