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 γ⁎γ⁎→ππ.
Highlights
The limiting factor in the accuracy of the Standard-Model prediction for the anomalous magnetic moment of the muon aμ = (g − 2)μ/2 is control over hadronic uncertainties [1,2]
In contrast to previous approaches [9,10,11,12,13,14,15,16,17,18,19,20,21], this formalism aims at providing a direct link between data and the hadronic light-by-light (HLbL) contribution to aμ
While high-energy data will be highly welcome when it comes to addressing the asymptotic behavior, to fix the parameters of the approach data in the low-energy region say for center-of-mass energies below 1–1.5 GeV will be most beneficial and are expected to have the largest potential impact on the HLbL contribution
Summary
Substantially more involved than that for HVP, we present here an overview of this approach leaving aside all theoretical details, and emphasize which measurements can help constrain the required hadronic input At present such an overview can only be obtained after studying several different theoretical papers. It is, essential that experimentalists become fully aware that some measurements may have a substantial and model-independent impact on a better determination of the HLbL contribution to aμ. Essential that experimentalists become fully aware that some measurements may have a substantial and model-independent impact on a better determination of the HLbL contribution to aμ This is the main aim of the present letter
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