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+ | ====== TTP95-26 ANGULAR DISTRIBUTIONS OF MASSIVE QUARKS AND LEPTONS CLOSE TO THRESHOLD ====== | ||

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+ | <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. | ||

+ | </hidden> | ||

+ | |**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]] | | ||

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