Measurement of the Branching Ratios of Kμ2+, Kπ2+, Ke3+, and Kμ3+

Abstract

In an experiment performed at the Princeton-Pennsylvania Accelerator with scintillation counters and spark chambers, we have determined the branching ratios for the $K^{+}$ decay modes ${K_{\mu 2}}^{+}$, ${K_{\pi 2}}^{+}$, ${K_{\mu 3}}^{+}$, and ${K_{e3\mathrm{}}}^{+}$. For each event, we measured the momentum and range of the charged secondary and the time interval between the arrival of the $K^{+}$ and its decay. The momentum was measured in thin-foil spark chambers placed in a magnetic field. The range was then measured in a thick-plate spark chamber in which all charged products from $K^{+}$ decay were stopped. $K^{+}$ decays in flight were eliminated through use of the timing information. The solid angle and detection efficiency of the apparatus were constant over the momentum interval 130 to 260 $\frac{\mathrm{MeV}}{c}$. Based on approximately 23 000 measured events, our values for the branching ratios are (63.34±0.44)% for ${K_{\mu 2}}^{+}$, (20.59±0.40)% for ${K_{\pi 2}}^{+}$, (4.97±0.16)% for ${K_{e3\mathrm{}}}^{+}$, and (3.82±0.29)% for ${K_{\mu 3}}^{+}$. These values have been determined by using for the $\tau$ and ${\tau }^{\prime }$ branching ratios (5.58±0.08)% and (1.70±0.055)%, respectively. A table of weighted averages of all $K^{+}$ branching-ratio measurements is included.