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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 ​ ====== + + + <​hidden 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]] ​  | + | |