Measurement of $K^+ \to \pi^0 \pi^0 e^+ \nu$ ($K_{e4}^{00}$) decay using   stopped positive kaons
  The $K^+ \to \pi^0 \pi^0 e^+ \nu$ ($K_{e4}^{00}$) decay has been measured with stopped positive kaons for a data sample of 216 events. A comparison of the observed spectra with a Monte Carlo simulation determined the $K_{e4}^{00}$ form factor. The results are compatible with the $K^+ \to \pi^+ \pi^- e^+ \nu$ data, as estimated from the $\Delta I=1/2$ rule. We also established that the $K_{e4}^{00}$ channel can be used to determine the $\pi$-$\pi$ scattering lengths. 
S. Shimizu, K. Horie, M. Aliev, Y.Asano, T. Baker, P. Depommier, M.   Hasinoff, Y. Igarashi, J. Imazato, A.P. Ivashkin, M.M....