Reactions of StoppingK−in Helium

Branching ratios have been measured for reactions initiated by negative kaons coming to rest in a helium bubble chamber. The data were obtained from an analysis of ∼1000 events found in a careful scan using a very limited fiducial volume. Charged-$\Sigma$ emission accounts for (30.8±3.2)% of the absorptions and $\frac{\Lambda }{{\Sigma }^0}$ emission for (69.2±6.6)%. Evidence for $\Sigma$-to-$\Lambda$ conversion is clearly seen in the events with a visible $\Lambda +{\pi }^{-}$, and (66±9)% of this final state results from such a process. Multinucleon (i.e., nonpionic) absorption is found to occur in (16.5±2.6)% of the events, which is similar to the results reported from studies using heavy-liquid bubble chambers and nuclear emulsion. In general, the kinematic spectra for single-nucleon absorption events agree well with the predictions of a simple impulse approximation. The ratio of $K^{-}$ capture on neutrons to that on protons is examined using the $\Lambda {\pi }^{-}{\mathrm{He}}^3$ and the $\Lambda {\pi }^0{\mathrm{H}}^3$ final states. The data for charged- and neutral-particle emission are consistent with the predictions of isospin invariance for kaon absorption in ${\mathrm{He}}^4$.