Determination of the Parity of the Neutral Pion via the Four-Electron Decay

TL;DR

This study confirms the negative parity of the neutral pion through its four-electron decay mode, providing precise measurements of its form factor, branching ratio, and limits on scalar contributions, using a large data sample from the KTeV experiment.

Contribution

The paper provides the first precise determination of the neutral pion's parity via the four-electron decay mode with a large data sample and detailed form factor analysis.

Findings

Confirmed negative parity of the neutral pion.

Measured the branching ratio as (3.26 ± 0.18) x 10^(-5).

Placed a limit on scalar contributions to the decay amplitude.

Abstract

We present a new determination of the parity of the neutral pion via the double Dalitz decay pi^0 -> e+ e- e+ e-. Our sample, which consists of 30511 candidate decays, was collected from K_L -> pi0 pi0 pi0 decays in flight at the KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the negative pi^0 parity, and place a limit on scalar contributions to the pi^0 -> e+ e- e+ e- decay amplitude of less than 3.3% assuming CPT conservation. The pi^0 gamma* gamma* form factor is well described by a momentum-dependent model with a slope parameter fit to the final state phase space distribution. Additionally, we have measured the branching ratio of this mode to be B(pi^0 -> e+ e- e+ e-) = (3.26 +- 0.18) x 10^(-5).