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

International audienceA 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