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 — preprints:1995:ttp95-26 [2016/03/17 11:03] (current) Line 1: Line 1: + ====== TTP95-26 ANGULAR DISTRIBUTIONS OF MASSIVE QUARKS AND LEPTONS CLOSE TO THRESHOLD  ====== + + + Predictions for the angular distribution of massive quarks and + leptons are presented, including QCD and QED corrections. Recent + results for the fermionic part of the two-loop corrections to the + electromagnetic form factors are combined with the BLM scale fixing + prescription. Two distinctly different scales arise as arguments of + $\alpha_s(\mu^2)$ near threshold: the relative momentum of the + quarks governing the soft gluon exchange responsible for the Coulomb + potential, and a large momentum scale approximately equal to twice + the quark mass for the corrections induced by transverse gluons. + Numerical predictions for charmed, bottom, and top quarks are given. + One obtains a direct determination of $\alpha_{\mbox{\it\scriptsize + V}}(Q^2)$, the coupling in the heavy quark potential, which can be + compared with lattice gauge theory predictions. The corresponding + QED results for $\tau$ pair production allow for a measurement of + the magnetic moment of the $\tau$ and could be tested at a future + $\tau$-charm factory. + + |**S.J. Brodsky, A.H. Hoang, J.H. K\"uhn and T. Teubner,**  | + |** Phys. Lett. B359 355-361 1995  **  | + | {{preprints:1995:ttp95-26.pdf|PDF}} {{preprints:1995:ttp95-26.ps|PostScript}} [[http://arxiv.org/abs/hep-ph/9508274|arXiv]]   | + | |