Summing next-to-next-to-leading logarithms in b → c transitions at zero recoil
نویسنده
چکیده
Weak b → c transitions are described by QCD currents c̄Γb with Γ = γ and γ5γ . If we are only interested in their matrix elements for pb = mbv + k, pc = mcv ′ + k, where the residual momenta k, k are small as compared to the heavy-quark masses mc,b, then we may expand these QCD currents in HQET operators of the form c̄v′ · · · bv with the appropriate quantum numbers divided by powers of mc,b. The coefficients are calculated by matching. This is descussed, e.g., in the review [1] or in the textbook [2]. In this paper we consider the zero-recoil case v = v. Then, in the v rest frame,
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