Non-leptonic B-decays in and beyond QCD Factorisation

Abstract

This thesis examines the non-leptonic B-decays within QCD factorisation and beyond, to challenge the assumptions and limitations of the method. We analyse the treatment of the distribution amplitudes of light mesons and present a new model described by simple physical parameters. The leading twist distribution amplitudes of light mesons describe the leading non-perturbative hadronic contributions to exclusive QCD reactions at large energy transfer, for instance electromagnetic form factors. Importantly, they also enter into the two-body B decay amplitudes described by QCD factorisation. They cannot be calculated from first principles and are described by models based on a fixed-order conformal expansion, which is not always sufficient in phenomenological applications. We derive new models that are valid to all orders in the conformal expansion and characterised by a small number of parameters related to experimental observables.Motivated by the marginal agreement between the QCD factorisation results with the experimental data, in particular for $B\to\pi\pi$, we scrutinise the incalculable non-factorisable corrections to charmless non-leptonic decays. We use the available results on $B\to\pi\pi$ to extract information about the size and nature of the required non-factorisable corrections that are needed to reconcile the predictions and data. We find that the best-fit scenarios do not give reasonable agreement to $2\sigma$ until at least a 40% non-factorisable contribution is added. Finally we consider the exclusive $B\to V\gamma$ decays, where we analyse the recently updated experimental data within QCD factorisation and present constraints on generic supersymmetric models using the mass insertion approximation.