b decays: a factory for hidden charm multiquark states

Abstract

We assume that the two hidden charm pentaquark discovered at $LHCb$ are built by the three light quarks and the $c\bar{c}$ pair, both colour octets. in relative P-wave for the ${\frac{5}{2}}^{+}$ state and by the eigenvectors of the chromomagnetic interaction for the five constituents in S-wave for the four ${\frac{3}{2}}^{-}$ state with masses $4360$, $4410$, $4490$ and $4560$ MeV . The "open channel" $p$ $J/\psi$ has large components along the two first states and so appear as the $4380$ resonance and the ${\Lambda }_c$ ${\bar{D}}^{0\ast }$ and ${\Sigma }_c$ ${\bar{D}}^{\ast }$ are "open channels" for the lower and higher resonances, respectively. The expectation for their strange isoscalar partners is to have a mass larger by an amount of the order or smaller than the $M_{\Lambda }-M_N$ mass difference. We account for the small width of the ${\frac{5}{2}}^{+}$, since its decay needs the exchangeof a gluon and stress that the decays of particles with "beauty" provide the best experimental framework for the discovery of hidden charm multiquarks. The relevance of the production mechanics shows the reason why only some of the states with non minimal number of constituents have been found.

Comments: 12 pages