Study Of ?~0??e~+e~- And J/???e~+e~- Decay At BES?

The electromagnetic?EM?Dalitz decay of light pseudoscalar meson??⁰,?,?'?plays an important role in revealing the structure of hadrons and the mechanism of the interactions between hadrons and photons.By the Dalitz decay of light pseudoscalar meson,the form factor and the slope of it can be measured with great precision.Based on a sample of 1.3 billion J/? events collected with the BESIII detector,we study the electromagnetic Dalitz decays of ?⁰??e⁺e^-through J/???⁺?^-?⁰??⁰??e⁺e^-?.Different expressions of form factor are attempted to describe the transition form the e⁺e⁺invariant mass spectrum.The slope of form factor for ?⁰(b_?⁰)to be b_?⁰=0.025±0.032.The slope of form factor has been measuered without desired accuracy.With a big data sample,it's tempting for us to study the behavior of form factor.Based on?225.3±2.8?×10⁶ J/? data,the electromagnetic?EM?Dalitz decay of J/???e⁺e^- has been studied.And the branching fractions was determined to be B?J/???e⁺e^-?=?1.16±0.09?×10^-5.Based on a greater sample of 1.3 billion J/? events collected with the BESIII detector,we study the electromagnetic Dalitz decays of J/???e⁺e^- more precisely.And a search for dark photon U is performed.The branching fractions is measured to B?J/???e⁺e^-?=1.44±0.06)×10^-5.