Study of 𝑒+⁢𝑒− →𝜋+⁢𝜋−⁢𝐽/𝜓 and Observation of a Charged Charmoniumlike State at Belle

Abstract

The cross section for 𝑒+⁢𝑒− →𝜋+⁢𝜋−⁢𝐽/𝜓 between 3.8 and 5.5 GeV is measured with a 967  fb−1 data sample collected by the Belle detector at or near the 𝛶⁡(𝑛⁢𝑆) (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 parametrization 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⁢(𝜋±⁢𝐽/𝜓) mass spectrum with 5.2⁢𝜎 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 charmoniumlike state.