Status of Measurement of R Value at BESIII

摘要

The R value is important for muon magnetic moment a _(μ)and QED running coupling constant evaluated at Z pole, is useful to extract resonance parameters. BESIII experiment collected about 130 energy points between 2.0GeV and 4.6GeV for a precise measurement of R value. The status of R measurement at BESIII is reported in this paper.