Study of e(+)e(-) -> pi(+)pi(-) J/psi and Observation of a Charged Charmoniumlike State at Belle

Abstract

The cross section for e+e−→π+π−J/ψ 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 Υ(nS) (n=1, 2, ..., 5) resonances. The Y(4260) state is observed, and its resonance parameters are determined. In addition, an excess of π+π−J/ψ 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)→π+π−J/ψ decays, a structure is observed in the $M(\pi^\pm\jpsi)$ mass spectrum with 5.2σ significance, with mass M=(3894.5±6.6±4.5)MeV/c2 and width Γ=(63±24±26) MeV/c2, where the errors are statistical and systematic, respectively. This structure can be interpreted as a new charged charmonium-like state.