On a possible measurement of alpha_s from B-Bbar correlations in Z^0 decay

Abstract

Motivated by recent preliminary results from the SLD Collaboration on the measurement of angle-dependent B-Bbar energy correlations in Z^0 -> b bbar events, we propose a class of observables that can be computed as a power expansion in the strong coupling constant alpha_s, of order alpha_s at the Born level and that can be used for a precision measurement of alpha_s(M_Z). We compute their next-to-leading order O(alpha_s^2) corrections in the strong coupling constant, including exactly quark-mass effects. We show that, in the theoretical evaluation of these quantities, large logarithms of the ratio of the mass of the final quark over the centre-of-mass energy cancel out. Thus, these variables have a well-behaved perturbative expansion in alpha_s(M_Z). We study the theoretical uncertainties due to the renormalization-scale dependence and the quark-mass scheme and we address the question of which mass scheme is more appropriate for these variables.