A Measurement of the Branching Ratio of $\ddot{I}{€}^0$ Dalitz Decay using $K_L\to \ddot{I}{€}^0\ddot{I}{€}^0\ddot{I}{€}^0$ Decays

Abstract

We present a measurement of $B(\ddot{I}{€}^0\to e^{+}{e}^{-}{\hat{I}}^3)/B(\ddot{I}{€}^0\to {\hat{I}}^3{\hat{I}}^3)$, 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 $K_L$ decays in flight; the measurement is based on about 60 thousand $K_L\to \ddot{I}{€}^0\ddot{I}{€}^0\ddot{I}{€}^0\to {\hat{I}}^3{\hat{I}}^3{\hat{I}}^3{\hat{I}}^3{e}^{+}{e}^{-}{\hat{I}}^3$ decays. We normalize to $K_L\to \ddot{I}{€}^0\ddot{I}{€}^0\ddot{I}{€}^0\to 6{\hat{I}}^3$ decays. We find $B(\ddot{I}{€}^0\to e^{+}{e}^{-}{\hat{I}}^3)/B(\ddot{I}{€}^0\to {\hat{I}}^3{\hat{I}}^3)$ $(m_{e^{+}{e}^{-}}$ > 15 MeV/$c^2)$ = $[3.920\pm 0.016(stat)\pm 0.036(syst)]\times 10^{-3}$. 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 $B(\ddot{I}{€}^0\to e^{+}{e}^{-}{\hat{I}}^3)/B(\ddot{I}{€}^0\to {\hat{I}}^3{\hat{I}}^3)=[1.1559\pm 0.0047(stat)\pm 0.0106(syst)]$%. This result is consistent with previous measurements and the uncertainty is a factor of three smaller than any previous measurement.

11 pages, 7 figures; v2 accepted version