A measurement of the π⁰, η and η′ electromagnetic form factors

Abstract

We present measurement of the π⁰γ^*γ, ηγ^*γ and η′γ^*γ form factors. The π⁰-form factor is for the first time observed in the space-like region. The transition form factor of the η-meson is determined from its decay modes π⁺π⁻π⁰, π⁺π⁻γ and the neutral decay mode γγ. The decay of the η′ is observed in the decay channels ργ, ηπ⁺π⁻ with η→γγ and in the four charged prong final state stemming from ηπ⁺π⁻ with the η decaying into π⁺π⁻(π⁰/γ). All form factors agree well with a simple ρ-pole predicted by the vector meson dominance model and also with the QCD inspired Brodsky-Lepage model.