On the transition form factors of the axial-vector resonance f 1(1285) and its decay into e + e −
Marvin Zanke (Helmholtz-Institut für Strahlen- und Kernphysik (Theorie) and Bethe Center for Theoretical Physics, Universität Bonn, Bonn, 53115, Germany); Martin Hoferichter (Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, University of Bern, Sidlerstrasse 5, Bern, 3012, Switzerland); Bastian Kubis (Helmholtz-Institut für Strahlen- und Kernphysik (Theorie) and Bethe Center for Theoretical Physics, Universität Bonn, Bonn, 53115, Germany)
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 Landau–Yang 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 → 4π, 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.
