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

We present a new determination of the parity of the neutral pion via the double Dalitz decay { pi}{ sup0} {yields} e{ sup+}e{ sup-}e{ sup+}e{ sup-}. Our sample, which consists of 30 511 candidate decays, was collected from K{sub L} {yields} { pi}{ sup0}{ pi}{ sup0}{ pi}{ sup0} decays in flight at the KTeV-E799 experiment at Fermi National Accelerator Laboratory. We confirm the negative { pi}{ sup0} parity, and place a limit on scalar contributions to the { pi}{ sup0} {yields} e{ sup+}e{ sup-}e{ sup+}e{ sup-} decay amplitude of less than 3.3% assuming CPT conservation. The { pi}{ sup0}{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}{ sup0} {yields} e{ sup+}e{ sup-}e{ sup+}e{ sup-}) = (3.26 {+-} 0.18) x 10{ sup-5}.