The ccbar Pentaquarks by a Quark Model

TL;DR

This paper uses a quark cluster model to explore possible pentaquark states with hidden charm, predicting structures that may explain recent LHCb pentaquark observations.

Contribution

It introduces a detailed quark cluster model analysis of hidden-charm pentaquarks, identifying configurations that produce states near observed resonance energies.

Findings

Identifies a color-octet isospin-1/2 spin-3/2 $uud$ configuration as attractive.

Predicts one bound state, two resonances, and a cusp near $ ext{Σ}_c^{(*)}ar{ ext{D}}^{(*)}$ thresholds.

Suggests these structures may correspond to LHCb pentaquark signals.

Abstract

Recent LHCb experiments have shown us that there are two resonances in the $J/\psi p$ channel in the $\Lambda_b$ decay, whose spin and parity are most probably (3/2$^-$ 5/2$^+$). In this work, we investigate the $I(J^P)=1/2(1/2^-)$, $1/2(3/2^-)$, and $1/2(5/2^-)$ $uudc{\bar c}$ pentaquark states by employing the quark cluster model. It is found that the color-octet isospin-1/2 spin-3/2 $uud$ configuration gives an attraction to such five-quark systems. This configuration together with the color-octet $c{\bar c}$ pair gives structures around the $\Sigma_c^{(*)}{\bar D}{}^{(*)}$ thresholds: one bound state, two resonances, and one large cusp are found in the $uudc{\bar c}$ negative parity channels. We argue that these resonances and cusp may correspond to, or combine to form, the negative parity pentaquark peak observed by LHCb.