An experimental study of the rare K+ meson decay K+ → pi+ e+e-

An experimental measurement of the rare kaon decay K+ → π+e+e- was made by a group of physicists from Brookhaven National Laboratory, the Swiss Institute for Nuclear Research, the University of Washington and Yale University. The experiment was performed at Brookhaven National Laboratory's Alternating Gradient Synchrotron in a series of data runs from 1985 to 1987. The Kπee decay is a second order weak which is sensitive to the (poorly understood) QCD corrections to the strangeness changing weak Hamiltonian. A total of 201 Kπee events were obtained, representing an increase in the world statistics of the decay by a factor of 5. An analysis of these events provided the first confirmation of the prediction that the decay proceeds via a vector interaction. The branching ratio for the decay was measured to be 3.4 ± 0.4 x 10-7, in approximate agreement with a previous measurements and within the errors of most theoretical predictions