Employing the decay chain K+ --> pi+pi0, pi0 --> e+e- we have observed the decay pi0 --> e+e-. With a signal sample of almost-equal-to 21 events we measure the branching ratio for pi0 --> e+e- to be (6.9 +/-2.3 +/- 0.6) x 10(-8), normalized to the decay K+ --> pi+pi0, pi0 --> e+e-gamma. This result is consistent with the unitarity lower bound and the published 90% confidence level upper limit of 13 x 10(-8).

We present results of an experiment in which approximately 500 events of the decay K + --> pi+ e+ e-were observed. We have measured the branching ratio for K(pi-ee)+ to be (2.75 +/- 0.23 +/- 0.13) x 10(-7) assuming a vector interaction with a form factor of lambda = 0.105 +/- 0.035 +/- 0.015. We have also found the branching ratio times decay probability for K + --> pi+ X0, X0 --> e+ e- to be less than 1.5 x 10(-8) (99% C. L.) over an X0 invariant mass range from 150 to 340 MeV/c2.

E777 at the Brookhaven AGS has published a final branching ratio limit for the lepton family violating decay K{sup +} {yields} {pi}{sup +}{mu}{sup +}e{sup {minus}} of 2.1 {times} 10{sup {minus}10} (90% C.L.). New results based on approximately 500 events of the G.I. M. suppressed decay K{sup +} {yields} {pi}{sup +}e{sup +}e{sup {minus}} have yielded a branching ratio of (2.75 {plus minus} 0.23 {plus minus} 0.13) {times} 10{sup {minus}7} assuming a vector interaction with, a form factor = 0.105 {plus minus} 0.035 {plus minus} 0.015. The branching ratio times decay probability for K{sup 0} {yields} {pi}{sup +} X{sup 0}, ,{sup 0} {yields} e{sup +}e{sup {minus}} was found to less than 1.5 {times} 10{sup {minus}8} (99% C.L.) in the e{sup +}e{sup {minus}} invariant mass range of 150 to 340 MeV/c. An approved second generation experiment sensitive to K{sup +} {yields} {mu}{sup +}e{sup {minus}} at the 10{sup {minus}12} level is discussed. 5 refs., 3 figs.

A search for the lepton-flavor number-violating decay ${K}^{+}$\ensuremath{\rightarrow}${\ensuremath{\pi}}^{+}$${\ensuremath{\mu}}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ has been conducted at the Brookhaven Alternating Gradient Synchrotron. No candidates have been found which would be consistent with this decay mode. An upper limit on the branching ratio is placed at 2.6\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$, which can be combined with our previous result to yield an upper limit of 2.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ at the 90% confidence level. A limit on the branching ratio for ${\ensuremath{\pi}}^{0}$\ensuremath{\rightarrow}${\ensuremath{\mu}}^{+}$${e}^{\mathrm{\ensuremath{-}}}$ of 1.6\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ (90% C.L.) is also established.

A search for the lepton family number violating decay K+ → π+μ+ e− has been performed. We established an upper limit on its branching ratio of 1.1 × 10−9 at the 90 % C.L. Measurements have also been made for the decay K+ → π+ e+ e−. A description of the measurement technique and some preliminary results are presented.

The progress of AGS Experiment 777, a search for K+→π+μ+e− is described. Results on the decay K+→π+A0, where A0 is a weakly interacting neutral particle that decays into e+e− and preliminary results on the direct decay K+→π+e+e− are presented as well as new limits on π0→μ+e−.

A search for the lepton-flavor violating decay K/sup +/..--> pi../sup +/..mu../sup +/e/sup -/ has been performed. Measurements have also been made of the branching ratio and decay particle distributions for the decay K/sup +/..--> pi../sup +/e/sup -/. A description of the measurement technique, and preliminary results are presented. 6 refs., 5 figs.

A search for the lepton-flavor violating decay K/sup +/..--> pi../sup +/..mu../sup +/e/sup -/ has been performed. Measurements have also been made of the branching ratio and decay particle distributions for the decay K/sup +/..--> pi../sup +/e/sup -/. A description of the measurement technique, and preliminary results are presented. 6 refs., 5 figs.

We report here on a search for the lepton-family-number-violating decay ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\mu}}^{+}{e}^{\ensuremath{-}}$. We found no evidence for this decay mode and we establish an upper limit on its branching ratio of 1.1\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}9}$ at the 90% confidence level (C.L.) for a uniform phase-space decay distribution. We also use this result to establish an upper limit for the branching ratio of the decay ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{e}^{\ensuremath{-}}$ of 7.8\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}8}$ (90% C.L.).

We have searched for the decay process ${K}^{+}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{A}^{0}$, where ${A}^{0}$ is any particle of mass less than 100 MeV/${\mathit{c}}^{2}$ decaying into ${e}^{+}{e}^{\ensuremath{-}}$. Upper limits for the branching ratio are given as a function of mass and lifetime of the ${A}^{0}$. For lifetimes shorter than ${10}^{\ensuremath{-}13}$ sec, a limit of 4.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}7}$ at the 90% confidence level is obtained.