New Determination of the Branching Ratios of K + -Meson Decay in Emulsion

A new experiment has been carried out to measure the branching ratios for ${K}^{+}$ decay in emulsion under improved conditions. The mesons were brought to rest in a 14-cc volume within a large stack of nuclear-research emulsion. The stack was designed so that the secondaries of the longest range could be followed to rest if they were emitted within certain cones. Some 700 such ${K}^{+}$ decays were chosen as the sample. The principal method for identifying the secondaries was by following the tracks to rest, thus avoiding many sources of systematic error. Ionization measurements were used to resolve ambiguities. The over-all scanning efficiency was found to be higher than 95%. The observed branching ratios for the ${K}_{\ensuremath{\mu}2}$, ${K}_{\ensuremath{\mu}3}$, ${K}_{\ensuremath{\pi}2}$, $\ensuremath{\tau}$, ${\ensuremath{\tau}}^{\ensuremath{'}}$, and ${K}_{e3}$ modes are (61.8\ifmmode\pm\else\textpm\fi{}2.9), (5.4\ifmmode\pm\else\textpm\fi{}0.9), (19.3\ifmmode\pm\else\textpm\fi{}1.6), (6.0\ifmmode\pm\else\textpm\fi{}0.4), (2.3\ifmmode\pm\else\textpm\fi{}0.6), and (5.3\ifmmode\pm\else\textpm\fi{}0.9)%, respectively. These results tend to reconcile the discrepancies between emulsion measurements and heavy-liquid-chamber data.