Heavy-quark symmetry partners of the Pc (4450) pentaquark

Abstract

The spectrum of heavy-hadron molecules is constrained by heavy-quark symmetry in its different manifestations. Heavy-quark spin symmetry for instance connects the properties of the ground and excited states of heavy hadrons, while heavy-antiquark-diquark symmetry connects the properties of heavy antimesons (D, D∗) and doubly heavy baryons (Ξcc, Ξcc∗). A prediction of these symmetries is that if the Pc(4450) is indeed a D∗Σc bound state, then there should be a series of D∗Σc∗, ΞccΣc, Ξcc∗Σc, ΞccΣc∗ and Ξcc∗Σc∗ partners. The concrete application of heavy-quark spin symmetry indicates that, if the Pc(4450) is a 32- D∗Σc molecule, the existence of a 52- D∗Σc∗ partner with similar binding energy - which we call Pc(4515), given its expected mass - is likely. Conversely, the application of heavy-antiquark-diquark symmetry indicates that the 0+ ΞccΣc, 1+ ΞccΣc∗, 2+ Ξcc∗Σc and 3+ Ξcc∗Σc∗ molecules are likely to bind too, with binding energies in the 20-30 MeV range.