On a possible measurement of αS from B– [formula omitted] correlations in Z0 decay

Abstract

Motivated by recent preliminary results from the SLD Collaboration on the measurement of angle-dependent B– B energy correlations in Z 0→b b ̄ events, we propose a class of observables that can be computed as a power expansion in the strong coupling constant α S, of order α S at the Born level and that can be used for a precision measurement of α S( M Z ). We compute their next-to-leading order O(α 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 α 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.