$R$ measurement and QCD studies at future super $τ-c$ factory

Abstract

We review status of R measurement and QCD studies at low energy range, discuss prospects for a super τ −charm factory in 2 − 7 GeV. With a high-luminosity e + e − collider, statistics are no longer problem for R measurement and a precision of 2% or even better is foreseen, that will lead to bring down the uncertainty of hadronic contribution to the QED running coupling constant ∆α had and the anomalous magnetic moment of the muon (a µ ); measure the strong coupling constant α s and the charm quark mass; improve the measurement of the resonance parameters of heavy charmonia. Huge data samples in 2 − 3 GeV will make it possible to study excited states of ρ, ω and φ, or exotic Y (2175); measure electromagnetic form factor of mesons and baryons; and measure fragmentation functions of hadrons.