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 the recent literature. Also analytical expressions are provided for some limiting cases of the corrections, previously calculated numerically.
|Original language||English (US)|
|Number of pages||10|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - Mar 20 2003|
Bibliographical noteFunding Information:
I thank A. Czarnecki, M. Shifman, and A. Vainshtein for enlightening discussions. This work is supported in part by the DOE grant DE-FG02-94ER40823.