B → s + γ: A QCD-consistent analysis of the photon energy distribution

The photon energy distribution in the inclusive b → s + γ transitions is a combination of two components: the first component, soft physics, is determined by the so-called primordial distribution function, while the second component, perturbative physics, is governed by hard gluon emission. A simple ansatz is suggested for the primordial distribution function which obeys the QCD constraints known so far. We then discuss in detail how hard gluon emission affects the energy distribution. An extension of the Sudakov approximation is worked out incorporating the Brodsky-Lepage-Mackenzie prescription and its generalizations. We explicitly calculate the marriage of nonperturbative and perturbative effects in the way required by OPE, introducing separation scale μ. A few parameters, such as m_b, and μ_π², affect the shape of the distribution and, thus, can be determined by matching to the experimental data. The data, still scarce, while not giving precise values for these parameters, yield consistency with theory: the current values of the above parameters lie within experimental uncertainty. On the theoretical side we outline a method allowing one to go beyond the practical version of OPE.