Heavy-quark symmetry partners of the $P_c(4450)$ pentaquark
Résumé
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.