Excitation energy spectra of the Lambda_c and Lambda_b baryons in a finite-size diquark model

TL;DR

This paper models the excitation energies of Lambda_c and Lambda_b baryons using a finite-size diquark potential approach, reproducing spectra well and highlighting the importance of diquark properties in heavy baryons.

Contribution

It introduces a finite-size diquark model to calculate heavy baryon excitation spectra, providing insights into diquark size and its role in baryon structure.

Findings

Diquark size estimated at 1.1 fm for certain parameters

Reproduces Lambda_c and Lambda_b spectra accurately

Does not explain the Lambda_c(2765) state

Abstract

The excitation energies of the $\Lambda_{c}$ and $\Lambda_{b}$ baryons are investigated in a finite-size diquark potential model, in which the heavy baryons are treated as bound states of a charm quark and a scalar-isoscalar diquark. The diquark is considered as a sizable object. The quark-diquark interaction is calculated as a sum of the quark-quark interaction which is assumed to be half of the quark-antiquark interaction for the color singlet. The potential parameters in the quark-antiquark interaction are fixed so as to reproduce the charmonium spectrum. We find the diquark size to be 1.1 fm for the diquark mass 0.5 GeV/c$^{2}$ to reproduce the $1p$ excitation energy of $\Lambda_{c}$. In this model, the $\Lambda_{c}$ and $\Lambda_{b}$ excitation spectra are reproduced well, while this model does not explain $\Lambda_{c}(2765)$, whose isospin nor spin-parity are unknown yet. Thus, the detailed properties of $\Lambda_{c}(2765)$ is very important to the presence of the diquark in heavy baryons as a effective constituent. We also discuss the $\Xi_{c}$ spectrum with the scalar strange diquark.