Addendum: A dispersive analysis of $$\varvec{\eta '\rightarrow \pi ^+\pi ^-\gamma }$$ and $$\varvec{\eta '\rightarrow \ell ^+\ell ^-\gamma }$$
Simon Holz (Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, University of Bern, Sidlerstrasse 5, Bern, 3012, Switzerland); Christoph Hanhart (Forschungszentrum Jülich, Institute for Advanced Simulation, Institut für Kernphysik, and Jülich Center for Hadron Physics, Jülich, 52425, 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 and Bethe Center for Theoretical Physics, Universität Bonn, Bonn, 53115, Germany)
In this addendum to Ref. [1] we show that the mismatch between the $$\rho $$ – $$\omega $$ mixing parameter $$\epsilon _{\rho \omega }$$ as extracted from $$\eta '\rightarrow \pi ^+\pi ^-\gamma $$ and $$e^+e^-\rightarrow \pi ^+\pi ^-$$ can be resolved by including higher orders in the expansion in $$e^2$$ in the description of the $$\eta '\rightarrow \pi ^+\pi ^-\gamma $$ decay. We repeat the analysis in this extended framework and update the numerical results accordingly.