Structure-dependent quantum electrodynamics in heavy meson physics

Abstract

The presence of electromagnetism in heavy meson systems cannot be neglected in the era of precision physics. While Quantum Electrodynamic (QED) effects are generally smaller than strong force contributions, factorisation properties are lost as photons may couple to light charged leptons. This can lead to mass-regulated collinear logarithms which, if left uncancelled, may lead to percent level corrections to decay rates.

In this thesis we explore QED effects in two settings. The main work of this thesis is a dispersive sum rule calculation of the leptonic B decay B⁻ -> l⁻ν(γ) to O(α_QED) in a new manifestly gauge-invariant framework. Particular attention is paid to the non-cancellation of collinear-type logarithms and structure-dependent effects beyond scalar QED. Virtual structure-dependent corrections are found to be +4.6(6)% and +2.9(2)% in the muon and tau channels respectively. Real structure-dependence lifts the helicity suppression found in the non-radiative decay and dominates in the electron and muon case.

The second setting in which QED effects are important is the mass difference between charged and neutral pseudoscalar mesons. While this is a well-studied problem we attack it for the first time using a double dispersion relation calculating the QED and linear quark mass shifts in a model independent way. This is a leading order ‘proof-of-principle’ calculation which we apply to the B, D and K systems giving good agreement with experiment albeit with large uncertainties.