On the transition form factors of the axial-vector resonance f1(1285) and its decay into e+e

A bstract Estimating the contribution from axial-vector intermediate states to hadronic light-by-light scattering requires input on their transition form factors (TFFs). Due to the L andau –Y ang theorem, any experiment sensitive to these TFFs needs to involve at least one virtual photon, which complicates their measurement. Phenomenologically, the situation is best for the f 1 (1285) resonance, for which information is available from e + e − → e + e − f 1 , f 1 → 4 π , f 1 → ργ , f 1 → ϕγ , and f 1 → e + e − . We provide a comprehensive analysis of the f 1 TFFs in the framework of vector meson dominance, including short-distance constraints, to determine to which extent the three independent TFFs can be constrained from the available experimental input — a prerequisite for improved calculations of the axial-vector contribution to hadronic light-by-light scattering. In particular, we focus on the process f 1 → e + e − , evidence for which has been reported recently by SND for the first time, and discuss the impact that future improved measurements will have on the determination of the f 1 TFFs.