# Nature of the $Y\left(4260\right)$: A light-quark perspective

Chen, Yun-Hua (School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China) ; Dai, Ling-Yun (School of Physics and Electronics, Hunan University, Changsha 410082, China) ; Guo, Feng-Kun (CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, China) (School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China) ; Kubis, Bastian (Helmholtz-Institut für Strahlen- und Kernphysik (Theorie) and Bethe Center for Theoretical Physics, Universität Bonn, 53115 Bonn, Germany)

16 April 2019

Abstract: The $Y\left(4260\right)$ 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 $Y\left(4260\right)$ from the light-quark perspective. We study the dipion invariant mass spectrum of the ${e}^{+}{e}^{-}\to Y\left(4260\right)\to J/\psi {\pi }^{+}{\pi }^{-}$ process and the ratio of the cross sections $\sigma \left({e}^{+}{e}^{-}\to J/\psi {K}^{+}{K}^{-}\right)/\sigma \left({e}^{+}{e}^{-}\to J/\psi {\pi }^{+}{\pi }^{-}\right)$. In particular, we consider the effects of different light-quark SU(3) eigenstates inside the $Y\left(4260\right)$. The strong pion–pion final-state interactions as well as the $K\overline{K}$ 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 $Y\left(4260\right)$ contains a large light-quark component. Our findings suggest that the $Y\left(4260\right)$ is neither a hybrid nor a conventional charmonium state, and they are consistent with the $Y\left(4260\right)$ having a sizeable $\overline{D}{D}_{1}$ component which, however, is not completely dominant.

Published in: Physical Review D 99 (2019)