ABSTRACT
QED atoms are composed of unstructured and point-like lepton pairs bound together by the electromagnetic force. The smallest and heaviest QED atom is formed by a τ+τ- pair. Currently, the only known atoms of this type are the e+e- and µ+e- atoms, which were discovered 64 years ago and remain the sole examples found thus far. We demonstrate that the Jτ (τ+τ- atom with JPC=1--) atom signal can be observed with a significance larger than 5σ including both statistical and systematic uncertainties, via. the process e+e-âX+Y-É (X,Y=e,µ,π,K, or ρ, and É is the missing energy due to unobserved neutrinos) with 1.5ab-1 data taken around the τ pair production threshold. The τ lepton mass can be measured with a precision of 1 keV with the same data sample. This is within one year's running time of the proposed super tau-charm facility in China or super charm-tau factory in Russia.
