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

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 $Δα_{had}$ 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.