Masses of Flavor Singlet Hybrid Baryons

Abstract

We study the possibility that four iso-singlet baryons $Λ_s(1405)$ $J^P=1/2^{-}$, $Λ_s(1520)$ $J^P=3/2^{-}$, $Λ_c(2593)$ $J^P=1/2^{-}$ and $Λ_c(2625)$ $J^P=3/2^{-}$ are hybrids: three quark one gluon states (udsg). We calculate the mass separations of the candidates, using a degeneracy-lifting hyperfine interaction from an effective single colored gluon exchange between the constituents. The correct ordering of masses is obtained (contrary to the case for the conventional interpretation as 3 quarks with L=1) and the splittings are plausible. The parity of these states is not measured, only assumed to be negative. In the hybrid picture, the lightest states are parity even and the parity odd counterparts lie about 300 MeV higher. Thus the hybrid ansatz predicts that either the parity of the $Λ(1405)$ etc is positive, or that there are undiscovered positive parity states about 300 MeV lower. We also remark that in this picture, the H-dibaryon mass may be around 1.5 GeV.