Emergence of a complete heavy-quark spin symmetry multiplet: seven molecular pentaquarks in light of the latest LHCb analysis

A recent analysis by the LHCb Collaboration suggests the existence of three narrow pentaquarklike states—the Pc(4312), Pc(4440), and Pc(4457)—instead of just one in the previous analysis [the Pc(4450)]. The closeness of the Pc(4312) to the D¯Σc threshold and the Pc(4440) and Pc(4457) to the D¯*Σc threshold suggests a molecular interpretation of these resonances. We show that these three pentaquarklike resonances can be naturally accommodated in a contact-range effective field theory description that incorporates heavy-quark spin symmetry. This description leads to the prediction of all the seven possible S-wave heavy antimeson-baryon molecules [that is, there should be four additional molecular pentaquarks in addition to the Pc(4312), Pc(4440), and Pc(4457)], providing the first example of a heavy-quark spin symmetry molecular multiplet that is complete. If this is confirmed, it will not only give us an impressive example of the application of heavy-quark symmetries and effective field theories in hadron physics, it will also uncover a clear and powerful ordering principle for the molecular spectrum, reminiscent of the SU(3)-flavor multiplets to which the light hadron spectrum conforms.