The onset of e+e- -> tau+ tau- at threshold revisited

الأصل · EN

The precise knowledge of the onset of the cross section σ(e+e- → τ+τ-) at the threshold is necessary for improving the accuracy of determination of the τ mass from the threshold measurements. The QED radiative corrections of relative order α and α², additional to the well known Coulomb factor, are considered in the threshold region. The correction terms of order α² are calculated, which contain coefficients enhanced by large parameters. As a result it is argued that the known O(α) corrections provide the accuracy of the description of the cross section close to 10⁻⁴, rather than 10⁻³ as claimed in a recent literature. Also analytical expressions are provided for some limiting cases of the corrections, previously calculated numerically.