Measurement of the Dalitz-decay branching ratio of the π0

The ratio B=Γ(π0 →e+ e-γ)/Γ(π0→γγ) is measured by comparing the production rates of the π0 in the two decay channels. The analysis is based on approximately four million hadronic decays of the Z boson recorded by the ALEPH detector in the years 1991 to 1995. The value of B is determined to be (1.140±0.041)%. A recalculation of the Particle Data Group world average gives rise to a slightly improved error, and moves the world average closer to the theoretical value. (orig.)