paper

Two-loop QCD corrections to transitions at zero recoil

arXiv:hep-ph/9603261 · doi:10.1103/PhysRevLett.76.4124

Abstract

Complete two-loop QCD corrections to transitions are presented in the limit of zero recoil. Vector and axial-vector coefficients are calculated analytically in the limit of equal beauty and charm masses, and a series appoximation is obtained for the general mass case. is crucial for the determination of the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element . The two-loop effects enhance the one-loop corrections by 21\%, removing a major theoretical uncertainty in the value of . Including two-loop QCD effects and previously neglected electroweak and Coulomb corrections we find .

8 pages, Revtex, one figure included

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