Measurement of the Dalitz-decay branching ratio of the π0

The ratio B = Gamma(pi(0) -> e(+)e(-)gamma)/Gamma(pi(0) -> gamma gamma) is measured by comparing the production rates of the pi(0) 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.