Study of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>e</mml:mi><mml:mo mathvariant="bold">+</mml:mo></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mo mathvariant="bold">−</mml:mo></mml:msup><mml:mo>→</mml:mo><mml:msup><mml:mi>π</mml:mi><mml:mo mathvariant="bold">+</mml:mo></mml:msup><mml:msup><mml:mi>π</mml:mi><mml:mo mathvariant="bold">−</mml:mo></mml:msup><mml:mi>J</mml:mi><mml:mo>/</mml:mo><mml:mi>ψ</mml:mi></mml:math>and Observation of a Charged Charmoniumlike State at Belle

Abstract

The cross section for ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}$ between 3.8 and 5.5 GeV is measured with a $967\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ data sample collected by the Belle detector at or near the $\ensuremath{\Upsilon}(nS)$ ($n=1,2,\dots{},5$) resonances. The $Y(4260)$ state is observed, and its resonance parameters are determined. In addition, an excess of ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}$ production around 4 GeV is observed. This feature can be described by a Breit-Wigner parametrization with properties that are consistent with the $Y(4008)$ state that was previously reported by Belle. In a study of $Y(4260)\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}$ decays, a structure is observed in the $M({\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}J/\ensuremath{\psi})$ mass spectrum with $5.2\ensuremath{\sigma}$ significance, with mass $M=(3894.5\ifmmode\pm\else\textpm\fi{}6.6\ifmmode\pm\else\textpm\fi{}4.5)\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and width $\ensuremath{\Gamma}=(63\ifmmode\pm\else\textpm\fi{}24\ifmmode\pm\else\textpm\fi{}26)\text{ }\text{ }\mathrm{MeV}/{c}^{2}$, where the errors are statistical and systematic, respectively. This structure can be interpreted as a new charged charmoniumlike state.