Heavy quark spin symmetry and heavy hadronic molecules

Abstract

In the heavy quark limit there is heavy quark spin symmetry. As a consequence, heavy hadrons or heavy quarkonia form spin multiplets. We argue that due to the symmetry, also heavy flavor hadronic molecules form spin multiplets, and the hyperfine splittings are the same as those between the heavy hadrons which are components of the molecules. Hence it provides a method to identify the nature of heavy hadronic molecules. As an example, we give predictions of the properties of an ηc′f0(980) bound state assuming the Y(4660) to be an S‐wave ψ′f0(980) shallow bound state. We also show that the enhancement observed in the Λc+Λc− invariant mass distribution might be the Y(4660).