Abstract
It is suggested that the recently reported charged charmoniumlike resonance $Z_c(4100)$ and the previously observed $Z_c(4200)$ are two states of hadrocharmonium, related by the charm quark spin symmetry in the same way as the lowest charmonium states $\eta_c$ and $J/\psi$. Namely, the $Z_c(4100)$ is (dominantly) the $\eta_c$ embedded in an light-quark excitation with quantum numbers of a pion, while the $Z_c(4200)$ is a similar four quark state containing $J/\psi$ instead of $\eta_c$. It is argued that this picture suggests certain relations between the properties of the two exotic resonances and a distinctive pattern of their decays that can be tested experimentally. It is also pointed out that due to the presence of a spatially compact $c \bar c$ charmonium the discussed exotic $Z_c$ states may be produced as resonances in the $s$ channel in $\bar p p$ annihilation.
Highlights
It is suggested that the recently reported charged charmoniumlike resonance Zcð4100Þ and the previously observed Zcð4200Þ are two states of hadrocharmonium, related by the charm quark spin symmetry in the same way as the lowest charmonium states ηc and J=ψ
The charged charmoniumlike resonance Zcð4100Þ most recently reported [1] in the channel ηcπ in the decays B0 → Zcð4100Þ−Kþ → ηcπ−Kþ is the latest addition to the growing set of intriguing exotic states observed at the onset of the charm-anticharm and bottom-antibottom open flavor thresholds
The existing theoretical approaches to the description of such four quark states concentrate on finding some simplification in the cases where the multiquark dynamics can be approximated by dominant two-body correlations. (Recent reviews of the experimental data and of the theoretical approaches can be found in Refs. [2,3,4].) It is quite natural to expect that such dominant correlations are likely to be different in different resonances
Summary
It is suggested that the recently reported charged charmoniumlike resonance Zcð4100Þ and the previously observed Zcð4200Þ are two states of hadrocharmonium, related by the charm quark spin symmetry in the same way as the lowest charmonium states ηc and J=ψ. The purpose of the present paper is to point out that the most recently found resonance Zcð4100Þ and the previously observed one Zcð4200Þ [13] are likely two states of hadrocharmonium and are related to each other in that they have the same “hosting” excited light matter state, and the embedded charmonium states are the heavy quark spin symmetry (HQSS) partners: respectively ηc and J=ψ.
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