Abstract
We present our model-independent and data-driven method to describe pseudoscalar meson transition form factors in the space- and (low-energy) time-like regions. The method is general and conforms a toolkit applicable to any other form factor, of one and two variables, with the potential to include both high- and low-energy QCD constraints altogether. The method makes use of analyticity and unitary properties of form factors, it is simple, systematic and can be improved upon by including new data. In the present discussion, the method is used to show the impact of experimental data for precision calculations in the low-energy sector of the Standard Model. In particular, due to its relevance for New Physics searches, we have considered the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon (the pseudoscalar exchange contribution), the pseudoscalar decays into lepton pairs, and the determination of the mixing parameters of the $\eta$ and $\eta'$ system. For all of them we provide the most updated results in a data-driven manner.
Highlights
The pseudoscalar meson transition form factors (TFF) describe the effect of the strong interaction on the γ∗γ∗ − P transition and is represented by a function FPγ∗γ∗ (q21, q22) of the photon virtualities q21, and q22.From the experimental point of view, one can study the TFF from both space- and time-like energy regimes
Let us remark that form factors are not interesting by themselves as represent the knowledge of QCD in a nutshell, and for their important role on precision calculations of low-energy Standard Model observables such as the anomalous magnetic moment of the muon, the pseudoscalar decays into lepton pairs, the radius of the proton, etc, where deviations between the theoretical prediction and the experimental measure point towards an indirect search of New Physics phenomena
We developed it focusing on the need to properly introduce experimental data in a systematic manner in observables that manifest a discrepancy with the Standard Model calculation
Summary
Let us remark that form factors are not interesting by themselves as represent the knowledge of QCD in a nutshell, and for their important role on precision calculations of low-energy Standard Model observables such as the anomalous magnetic moment of the muon, the pseudoscalar decays into lepton pairs, the radius of the proton, etc, where deviations between the theoretical prediction and the experimental measure point towards an indirect search of New Physics phenomena. The experimental information on the TFFs together with the theoretical knowledge on their kinematic limits yield the opportunity for a nice synergy between experiment and theory in a simple, easy, systematic, and userfriendly method. This synergy is the purpose of our work.
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