Abstract
In this paper, we try to reveal the structure of the $Y(4660)$ from the light-quark perspective. We study the dipion invariant mass spectrum and the helicity angular distributions of the $e^+ e^- \to Y(4660) \to \psi(2S) \pi^+\pi^-$ process. In particular, we consider the effects of different light-quark SU(3) eigenstates inside the $Y(4660)$. The strong pion-pion final-state interactions as well as the $K\bar{K}$ coupled channel in the $S$-wave are taken into account model independently by using dispersion theory. We find that the light-quark SU(3) octet state plays a significant role in this transition, implying that the $Y(4660)$ contains a large light-quark component and thus might not be a pure conventional charmonium state. In the fit scheme considering both the SU(3) singlet and SU(3) octet states, two solutions are found, and both solutions reproduce the $\pi\pi$ invariant mass spectra well. New measurement data with higher statistics in the future will be helpful to better distinguish these two solutions.
Highlights
In recent years, a number of charmoniumlike states have been discovered and they challenge our current understanding of hadron spectroscopy
We note that the present data is limited in statistics, and a better distinction of Fits IIa and IIb requires new measurement data with higher statistics and smaller error bars
Through fitting to the data of the ππ invariant mass spectra and the angular cos θ distributions of eþe− → Yð4660Þ → ψð2SÞππ, we find that the lightquark SU(3) octet state plays a significant role in the Yð4660Þψð2SÞππ transition, which indicates that the Yð4660Þ contains a large light-quark component
Summary
A number of charmoniumlike states have been discovered and they challenge our current understanding of hadron spectroscopy Among these states, the Yð4660Þ was first observed in the initial-state radiation process eþe− → γISRψð2SÞπþπ− by the Belle Collaboration [1]. There is no charmonium state expected in the Yð4660Þ mass region with quantum numbers 1−− from the naive quark model [2], and the Yð4660Þ was not observed in eþe− → γISRJ=ψπþπ−. Such peculiar properties have initiated a lot of theoretical and experimental studies, see Refs.
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