First Observation Of J/Ψ Decaying To Four Leptons At BESⅢ

Using the data sample of 4.481 × 108 φ（3686） events collected with the BESIII,we performed an analysis on the decay modes of φ（3686）→π+π-J/φ,J/φ→l1+1-l1+l2-（l1,l2=e,μ）,e.g.e+e-e+e-,e+e-μ+μ-,μ+μ-μ+μ-,We observe the decay channels of Jφ/→e+e-e+e-and J/φ→e+e-μ+μ- for the first time,and their branching fractions are measured to be（5.17±0.39±0.35）× 10^-5 and （3.00±0.27±0.20）× 10^-5,respectively.The CP asymmetry magnitudes for these two channels are measured to be（0.098±0.070±0.077） and（0.086±0.093±0.060）,respectively.No significant signal is observed for J/φ→μ+μ-μ+μ- and the upper limit on the branching fraction is set to be 2.3 × 10-6 at 90%C.L..The two soft opposite charged pions from φ（3686）→π+π-J/φ are used to tag the J/φ mesons.With the tagged J/φ mesons from 106 million inclusive φ（3686）MC samples,the output branching fraction of J/φ→γηis in good agreement with the input one.So we have developed a method to study the J/φ decay with the φ（3 686） data set.