Probing the inner structures of the observed $Ξ_b$ and $Ξ_b'$ resonances

TL;DR

This paper addresses the internal structure of low-lying $Ξ_b$ and $Ξ_b'$ baryons by performing a systematic study of their strong decays in the $1P$- and $2S$-wave sectors using the $j$-$j$ coupling scheme. It compares the quark pair creation (QPC) model with the chiral quark model (ChQM) and analyzes both $\ λ$- and $\ρ$-mode excitations to map observed resonances like $Ξ_b(6087)$, $Ξ_b(6095/6100)$, and $Ξ_b(6227)$ to specific internal configurations. Key findings include the plausible identification of the $1P$-wave $λ$-mode states with the narrow $Ξ_b(6087)$ and $Ξ_b(6095)$, the potential assignment of $Ξ_b(6227)$ to $1P$-wave $ρ$-mode states (or certain $λ$-mode partners), and the prediction that many $2S$-wave states are relatively narrow (few to a few tens of MeV) while $2S$-wave $ρ$-mode states can be broader (tens to over a hundred MeV). The results provide a comprehensive decay-pattern reference that can guide experimental identification and future measurements of missing resonances in the bottom baryon sector.

Abstract

To shed light on the inner structure of the observed single-bottom strange baryons, in this work we systematically study the Okubo-Zweig-Iizuka allowed strong decay properties of $1P$- and $2S$-wave $Ξ_b$ and $Ξ_b'$ baryons within the $j-j$ coupling scheme in the framework of the quark pair creation model. For a comparison, we also give the predictions of the chiral quark model. The calculations indicate that: (i) The $1P$-wave $λ$-mode $Ξ_b$ states $Ξ_b|J^P=1/2^-,1\rangle_λ$ and $Ξ_b|J^P=3/2^-,1\rangle_λ$ are highly promising candidates for the observed state $Ξ_b(6087)$ and $Ξ_b(6095)/Ξ_b(6100)$, respectively. The $1P$-wave $ρ$-mode $Ξ_b$ states $Ξ_b|J^P=3/2^-,2\rangle_ρ$ and $Ξ_b|J^P=5/2^-,2\rangle_ρ$ are likely candidates for the state $Ξ_b(6227)$. Meanwhile, we cannot rule out the possibility that $Ξ_b(6227)$ could be a candidate of the $1P$-wave $λ$-mode $Ξ_b'$ state $Ξ_b'|J^P=3/2^-,2\rangle_λ$ or $Ξ_b'|J^P=5/2^-,2\rangle_λ$. (ii) For the other $1P$-wave $ρ$-mode $Ξ_b$ states and $1P$-wave $λ$-mode $Ξ_b'$ states, they may be moderate states with a width of several tens of MeV. Their main decay channels are $Ξ_bπ$, $Ξ_b'π$, $Ξ_b^*π$ or $Λ_b\bar{K}$. The width of the $1P$-wave $ρ$-mode $Ξ_b'$ states are slightly broader, approximately several tens to over one hundred MeV, and the dominant decay channels are $Ξ_b'π$, $Ξ_b^*π$, $Σ_bK$ or $Σ_b^*K$. (iii) The $2S$-wave $λ$-mode $Ξ_b$ and $Ξ_b'$ states are most likely to be relatively narrow state with a width of only a few to around ten MeV, and they mainly decay into $Ξ_b'π$ or $Ξ_b^*π$. In addition, the $2S$-wave $λ$-mode $Ξ_b'$ states may also mainly decay into the $1P$-wave $Ξ_b$ baryon via the pionic decay processes.

Figures (6)

• Figure 1: Partial and total strong decay widths of the $1P$-wave $\lambda$-mode $\Xi_b$ excitations as functions of their masses.
• Figure 2: Partial and total strong decay widths of the $1P$-wave $\lambda$-mode $\Xi_b'$ excitations as functions of their masses. Some decay channels are too small to show in figure.
• Figure 3: Partial and total strong decay widths of $\Xi_b'|J^P=3/2^-,2\rangle_{\lambda}$ as a function of the mixing angle. Some decay channels are too small to show in figure.
• Figure 4: Partial and total strong decay widths of the $1P$-wave $\rho$-mode $\Xi_b$ excitations as functions of their masses. Some decay channels are too small to show in figure.
• Figure 5: Partial and total strong decay widths of the $1P$-wave $\rho$-mode $\Xi_b'$ excitations as functions of their masses. Some decay channels are too small to show in figure.