Production of the ω vectorial meson through electrons-positrons annihilations (detection of π+π-π0). Indication of a ρ0-ω interference in the π+π- mode

The vectorial meson ω is obtained via virtual photons (of time type) coming from e+e- annihilations in the electrons positrons colliding ring (ACO) in Orsay. We have measured the coupling between the photon and the meson, in other words the partial width: Γ(ω → e+e-). It is difficult to achieve such a measurement because we need to detect e+e- pairs and π mesons coming from the decay of the ω produced from particles with strong interactions. The presence of hadrons in the final state may also disturb the ω → 3π mode. The use of the e+e- collider ring has allowed us to avoid both difficulties. We have got the following result: Γ(ω → e+e-) equals (1.0 ± 0.18) KeV, it is the first time that such a level of accuracy was obtained. As for the ρ-ω interference although a null effect can not be excluded, the value of the branching ratio B(ω → 2π) we have found [(3.3 ± 2.8;2.0)%) is coherent with theoretical predictions and previous experimental data