2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/179583An upper limit on the branching ratio for the decay $K^+ \! \rightarrow \! π^+ ν\overlineν$ is set at $2.4 \times 10^{-9}$ at the 90\% C.L. using pions in the kinematic region $214~{\rm MeV}/c < P_π< 231~{\rm MeV}/c$. An upper limit of $5.2 \times 10^{-10}$ is found on the branching ratio for decays $K^+ \! \rightarrow \! π^+ X^0$, where $X^0$ is any massless, weakly interacting neutral particle. Limits are also set for cases where $M_{X^0}>0$.uuencoded, compressed postscript, 9 pagesHigh Energy Physics - Experimenttext