Towards a data-driven analysis of hadronic light-by-light scattering

TL;DR

This paper reviews a dispersion theory framework for analyzing the hadronic light-by-light scattering contribution to the muon's magnetic moment, emphasizing experimental inputs and methods to constrain key form factors and amplitudes.

Contribution

It introduces a systematic dispersive approach to evaluate hadronic light-by-light scattering using experimental data for form factors and scattering amplitudes.

Findings

Identifies experimental processes to constrain pion transition form factors.

Highlights methods to estimate doubly-virtual pion-photon interactions.

Provides a formalism connecting experimental data to theoretical calculations.

Abstract

The hadronic light-by-light contribution to the anomalous magnetic moment of the muon was recently analyzed in the framework of dispersion theory, providing a systematic formalism where all input quantities are expressed in terms of on-shell form factors and scattering amplitudes that are in principle accessible in experiment. We briefly review the main ideas behind this framework and discuss the various experimental ingredients needed for the evaluation of one- and two-pion intermediate states. In particular, we identify processes that in the absence of data for doubly-virtual pion-photon interactions can help constrain parameters in the dispersive reconstruction of the relevant input quantities, the pion transition form factor and the helicity partial waves for $\gamma^*\gamma^*\to\pi\pi$.