Fitting the exotic hadron spectrum with an additional quark

Most of the exotic hidden-charm hadrons discovered over the last 20 years fit neatly into the quark model as normal mesons and baryons if the existence of a seventh flavor of quark is hypothesized. For the quark to reproduce the spectrum (mass, spin, parity) of exotic hadrons, it would have to have a mass of $\sim$2.9 GeV and a charge of $-\tfrac{1}{3}$. The observed production and decay modes of these hadrons can be reproduced by a model that also includes light scalar bosons.