Measurement of the branching ratio of π0 Dalitz decay using KL→π0π0π0 decays

We present a measurement of B(π0→e+e-γ)/B(π0→γγ), the Dalitz branching ratio, using data taken in 1999 by the E832 KTeV experiment at Fermi National Accelerator Laboratory. We use neutral pions from fully reconstructed KL decays in flight; the measurement is based on ∼60 thousand KL→π0π0π0→γγγγe+e-γ decays. We normalize to KL→π0π0π0→6γ decays. We find B(π0→e+e-γ)/B(π0→γγ) (me+e->15  MeV/c2)=[3.920±0.016(stat)±0.036(syst)]×10-3. Using the Mikaelian and Smith prediction for the e+e- mass spectrum, we correct the result to the full e+e- mass range. The corrected result is B(π0→e+e-γ)/B(π0→γγ)=[1.1559±0.0047(stat)±0.0106(syst)]%. This result is consistent with previous measurements, and the uncertainty is a factor of 3 smaller than any previous measurement.