The Pcs(4459) pentaquark from a combined effective field theory and phenomenological perspective

Abstract

The observation of the Pcs(4459) by the LHCb collaboration adds a new member to the set of known hidden-charm pentaquarks, which includes the Pc(4312) , Pc(4440) and Pc(4457). The Pcs(4459) is expected to have the light-quark content of a Λ baryon (I= 0 , S= - 1), but its spin is unknown. Its closeness to the D¯ ∗Ξ c threshold – 4478MeV in the isospin-symmetric limit – suggests the molecular hypothesis as a plausible explanation for the Pcs(4459). While in the absence of coupled-channel dynamics heavy-quark spin symmetry predicts the two spin-states of the D¯ ∗Ξ c to be degenerate, power counting arguments indicate that the coupling with the nearby D¯Ξc′ and D¯Ξc∗ channels might be a leading order effect. This generates a hyperfine splitting in which the J=32D¯ ∗Ξ c pentaquark will be lighter than the J=12 configuration, which we estimate to be of the order of 5-15MeV. We also point out an accidental symmetry between the Pcs(4459) and Pc(4440 / 4457) potentials. Finally, we argue that the spectroscopy and the J/ ψΛ decays of the Pcs(4459) might suggest a marginal preference for J=32 over J=12.