Study of $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ$ and Observation of a Charged Charmonium-like State at Belle

Abstract

The cross section for $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ$ between 3.8 GeV and 5.5 GeV is measured with a 967 fb${}^{-1}$ data sample collected by the Belle detector at or near the $\hat{I}\yen (nS)$ ($n=1,2,...,5$) resonances. The Y(4260) state is observed, and its resonance parameters are determined. In addition, an excess of $\ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ$ production around 4 GeV is observed. This feature can be described by a Breit-Wigner parameterization with properties that are consistent with the Y(4008) state that was previously reported by Belle. In a study of $Y(4260)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ$ decays, a structure is observed in the $M(π^\pm\jpsi)$ mass spectrum with $5.2\ddot{I}ƒ$ significance, with mass $M=(3894.5\pm 6.6\pm 4.5)\mathrm{MeV}/c^2$ and width $\hat{I}“=(63\pm 24\pm 26)$ MeV/$c^2$, where the errors are statistical and systematic, respectively. This structure can be interpreted as a new charged charmonium-like state.

10 pages, 5 figures, 2 tables, accepted by Phys. Rev. Lett