Abhay Deshpande

An experiment (E851) dedicated to study of the rare decay $K\sp+ \to \pi\sp{+}e\sp{+}e\sp{-}$, $K\sb{\pi ee}$, was performed in the spring of 1989 at Brookhaven National Laboratory’s Alternating Gradient Synchrotron (BNL-AGS). Using the ${\sim}$800 $K\sb{\pi ee}$ events gathered in E851, we have for the first time studied its angular correlations and measured the non vector hadronic current contribution to the otherwise presumed vector decay. We have also made a new measurement of its branching ratio (BR(2.87 $\pm$ 0.32(stat) $\pm$ 0.13(syst)) $\times$ 10$\sp{-7}$, and the momentum dependence of the vector form factor ($\lambda$ = 0.187 $\pm$ 0.036(stat) $\pm$ 0.010(syst)).

In addition to the study of the above decay, using 21 observed events of the decay chain, $K\sp{+} \to \pi\sp{+}\pi\sp{0}; \pi\sp{0} \to e\sp{+}e\sp{-}(K\sb{ee}$) we have measured, for the first time, the branching ratio of the decay $\pi\sp{0} \to e\sp{+}e\sp{-}$. The measured value, (8.0 $\pm$ 2.6(stat) $\pm$ 0.6(syst)) $\times$ 10$\sp{-8}$, is consistent with the unitarity lower bound and the previous published 90% confidence level upper Limit of 13 $\times$ 10$\sp{-8}$. In both branching ratio measurements, the branching ratio times decay probability for the decay $K\sp{+} \to \pi\sp{+}\pi\sp{0}; \pi\sp{0} \to e\sp{+}e\sp{-}\gamma$, $K\sb{dal}$ of (2.53 $\times 10\sp{-3}$), was used for normalization.