Novel method for identifying the heaviest QED atom.

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 ττ pair. Currently, the only known atoms of this type are the ee and μe atoms, which were discovered 64 years ago and remain the sole examples found thus far. We demonstrate that the J (ττ atom with J=1) atom signal can be observed with a significance larger than 5σ including both statistical and systematic uncertainties, via. the process ee→XYɆ (X,Y=e,μ,π,K, or ρ, and Ɇ is the missing energy due to unobserved neutrinos) with 1.5ab 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.