Measurement of the rare decay pi0 -> e+ e-
Abstract
The branching ratio of the rare decay pi0 -> e+ e- has been measured precisely, using the complete data set from the KTeV E799-II experiment at Fermilab. We observe 794 candidate pi0 -> e+ e- events using K0L -> 3pi0 as a source of tagged pi0's. The expected background is 52.7 +- 11.2 events, predominantly from high e+ e- mass pi0 -> e+ e- gamma decays. We have measured B[(pi0 -> e+ e-), (me+e-/mpi0)2 > 0.95] = 6.44 +- 0.25(stat) +- 0.22(syst) x10(-8), which is above the unitary bound from pi0 -> gamma gamma and within the range of theoretical expectations from the standard model.
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