Possible interpretation of the $Z_b$(10610) and $Z_b$(10650) in a chiral quark model

TL;DR

This paper investigates the nature of the $Z_b$(10610) and $Z_b$(10650) resonances as molecular states of heavy mesons using a chiral quark model, predicting several bound states and suggesting experimental searches for validation.

Contribution

It provides a theoretical interpretation of the $Z_b$ resonances as molecular states and predicts new bound states within the chiral quark model framework.

Findings

Bound states $Bar{B}^*$ and $B^*ar{B}^*$ match $Z_b$(10610) and $Z_b$(10650)

Additional bound states predicted in other quantum configurations

Deeper bound states found when including hidden color channels

Abstract

Motivated by the two charged bottomonium-like resonances $Z_b$(10610) and $Z_b$(10650) newly observed by the Belle collaboration, the possible molecular states composed of a pair of heavy mesons, $B\bar{B}, B\bar{B}^*, B^*\bar{B}^*, B_s\bar{B}$, etc (in S-wave), are investigated in the framework of chiral quark models by the Gaussian expansion method. The bound states $B\bar{B}^*$ and $B^*\bar{B}^*$ with quantum numbers $I(J^{PC})=1(1^{+-})$, which are good candidates for the $Z_b(10610)$ and $Z_b(10650)$ respectively, are obtained. Other three bound states $B\bar{B}^*$ with $I(J^{PC})=0(1^{++})$, $B^*\bar{B}^*$ with $I(J^{PC})=1(0^{++}), 0(2^{++})$ are predicted. These states may be observed in open-bottom or hidden-bottom decay channel of highly excited $\Upsilon$. When extending directly the quark model to the hidden color channel of the multi-quark system, more deeply bound states are found. Future experimental search of those states will cast doubt on the validity of applying the chiral constituent quark model to the hidden color channel directly.