Novel pentaquark picture for singly heavy baryons from chiral symmetry

Abstract

We propose a new type of structure for singly heavy baryons of $Qqq\bar{q}q$ in addition to the conventional one of $Qqq$. Based on chiral symmetry of the light quarks, we show that the $Qqq\bar{q}q$ baryon offers a novel picture for heavy quark spin-singlet and flavor-antisymmetric baryons. By making use of the effective Lagrangian approach, we find $\Lambda_c(2765)$ and $\Xi_c(2967)$ are mostly $Qqq\bar{q}q$ while $\Lambda_c(2286)$ and $\Xi_c(2470)$ are mostly $Qqq$. The masses of negative-parity baryons are predicted. We also derive a sum rule and the extended Goldberger-Treiman relation that the masses of the baryons satisfy. Furthermore, a mass degeneracy of parity partners of the baryons with the restoration of chiral symmetry is discussed. These are the unique features that the conventional picture of radial excitation in the quark model does not accommodate. Our findings provide useful information not only for future experiments but also for future lattice simulations on diquarks.