Abstract
The $Y(4260)$ has been one of the most puzzling pieces among the so-called $XYZ$ states. In this paper, we try to gain insights into the structure of the $Y(4260)$ from the light-quark perspective. We study the dipion invariant mass spectrum of the $e^+ e^- \to Y(4260) \to J/\psi \pi^+\pi^-$ process and the ratio of the cross sections ${\sigma(e^+e^- \to J/\psi K^+ K^-)}/{\sigma(e^+e^- \to J/\psi \pi^+\pi^-)}$. In particular, we consider the effects of different light-quark SU(3) eigenstates inside the $Y(4260)$. The strong pion-pion final-state interactions as well as the $K\bar{K}$ coupled channel in the $S$-wave are taken into account in a model-independent way using dispersion theory. We find that the SU(3) octet state plays a significant role in these transitions, implying that the $Y(4260)$ contains a large light-quark component. Our findings suggest that the $Y(4260)$ is neither a hybrid nor a conventional charmonium state, and they are consistent with the $Y(4260)$ having a sizeable $\bar D D_1$ component which, however, is not completely dominant.
Highlights
The nature of the vector charmoniumlike state Yð4260Þ has remained controversial since its discovery in the initialstate radiation process eþe− → γISRJ=ψπþπ− [1]
We find that the SU(3) octet state plays a significant role in these transitions, implying that the Yð4260Þ contains a large light-quark component
In this work we perform fits taking into account the experimental data sets of the ππ invariant mass distributions of eþe− → J=ψπþπ− and the ratios of the cross sections σðeþe− → J=ψKþK−Þ=σðeþe− → J=ψπþπ−Þ measured at two energy points E 1⁄4 4.23 GeV and E 1⁄4 4.26 GeV by DP or the BO parametrizations
Summary
The nature of the vector charmoniumlike state Yð4260Þ has remained controversial since its discovery in the initialstate radiation process eþe− → γISRJ=ψπþπ− [1]. There is no room for the Yð4260Þ in the charmonium spectrum predicted in the naive quark model [2], and the Yð4260Þ does not show strong couplings to ground-state open-charm decay modes [3], which is unexpected for conventional vector ccstates above the DDthreshold. Such peculiar properties have initiated a lot of theoretical and experimental studies, see Refs.
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