Radiative leptonic decays of B mesons in QCD

TL;DR

This paper calculates form factors for radiative leptonic B meson decays at high photon energies using perturbative QCD and heavy quark effective theory, providing a method to determine |V_{ub}| from decay spectra.

Contribution

It introduces a combined perturbative and effective theory approach to compute form factors and resums Sudakov logarithms for radiative B decays, enabling |V_{ub}| extraction.

Findings

Form factors expressed as convolutions with B meson wave functions.

Explicit one-loop calculation of hard scattering amplitude.

Resummation of Sudakov double logarithms to all orders.

Abstract

We compute the form factors parametrizing radiative leptonic decays of heavy mesons B^+\to\gamma e^+\nu for photon energies much larger than \Lambda_{QCD}, where perturbative QCD methods for exclusive processes can be combined with the heavy quark effective theory. The form factors can be reliably obtained in this region in an expansion in powers of \Lambda/E_\gamma. The leading term in this expansion displays an additional spin symmetry manifested in the equality of form factors of vector and axial currents. The leading twist form factors can be written as the convolution of the B meson light-cone wave function with a hard scattering amplitude, which is explicitly calculated to one-loop order. The Sudakov double logarithms of the form (\frac{\alpha_s}{\pi}\log^2\frac{2E_\gamma}{\Lambda})^n are resummed to all orders. As an application we present a method for determining the CKM matrix element |V_{ub}| from a comparison of photon spectra in B and D radiative leptonic decays.