A measurement of the electromagnetic form factor of the eta meson and of the branching ratio for the eta Dalitz decay

Conversion $\phi $(1020) decays into $\pi^0 e^+ e^-$, $\eta$(550) $e^+e^-$ and $\eta $(550) into $e^+e^- \gamma$ from SND detector at VEPP

“…3.8 ± 1.8 1.6±2.0 -Theory (VDM) [1] 1.0 1.8 Previous measurement [3] -−0.7 ± 1.5 - Table 3: Experimental results for transition form factors slopes…”