The $$P_{cs}(4459)$$ pentaquark from a combined effective field theory and phenomenological perspective

Abstract

AbstractThe observation of the $$P_{cs}(4459)$$ P cs ( 4459 ) by the LHCb collaboration adds a new member to the set of known hidden-charm pentaquarks, which includes the $$P_c(4312)$$ P c ( 4312 ) , $$P_c(4440)$$ P c ( 4440 ) and $$P_c(4457)$$ P c ( 4457 ) . The $$P_{cs}(4459)$$ P cs ( 4459 ) is expected to have the light-quark content of a $$\Lambda $$ Λ baryon ($$I=0$$ I = 0 , $$S=-1$$ S = - 1 ), but its spin is unknown. Its closeness to the $${\bar{D}}^* \Xi _c$$ D ¯ ∗ Ξ c threshold – $$4478\,{\mathrm{MeV}}$$ 4478 MeV in the isospin-symmetric limit – suggests the molecular hypothesis as a plausible explanation for the $$P_{cs}(4459)$$ P cs ( 4459 ) . While in the absence of coupled-channel dynamics heavy-quark spin symmetry predicts the two spin-states of the $${\bar{D}}^* \Xi _c$$ D ¯ ∗ Ξ c to be degenerate, power counting arguments indicate that the coupling with the nearby $${\bar{D}} \Xi _c'$$ D ¯ Ξ c ′ and $${\bar{D}} \Xi _c^*$$ D ¯ Ξ c ∗ channels might be a leading order effect. This generates a hyperfine splitting in which the $$J=\tfrac{3}{2}$$ J = 3 2 $${\bar{D}}^* \Xi _c$$ D ¯ ∗ Ξ c pentaquark will be lighter than the $$J=\tfrac{1}{2}$$ J = 1 2 configuration, which we estimate to be of the order of $$5-15\,{\mathrm{MeV}}$$ 5 - 15 MeV . We also point out an accidental symmetry between the $$P_{cs}(4459)$$ P cs ( 4459 ) and $$P_c(4440/4457)$$ P c ( 4440 / 4457 ) potentials. Finally, we argue that the spectroscopy and the $$J/\psi \Lambda $$ J / ψ Λ decays of the $$P_{cs}(4459)$$ P cs ( 4459 ) might suggest a marginal preference for $$J = \tfrac{3}{2}$$ J = 3 2 over $$J = \tfrac{1}{2}$$ J = 1 2 .