Three- and four-nucleon absorption processes observed in the $K^-$-$^4$He reaction at rest

TL;DR

This study investigates non-mesonic absorption processes of stopped antikaons in helium-4, identifying three- and four-nucleon absorption channels through correlated Lambda-deuteron and Lambda-triton pairs, and estimates their branching ratios.

Contribution

It provides the first experimental identification and quantification of three- and four-nucleon absorption processes of antikaons at rest in helium-4.

Findings

Branching ratio for three-nucleon process: (0.9 ± 0.1(stat) ± 0.2(syst)) × 10^{-3}

Branching ratio for four-nucleon process: (3.1 ± 0.4(stat) ± 0.5(syst)) × 10^{-4}

Identification of non-mesonic absorption channels in helium-4

Abstract

Correlations of back-to-back coincident $\Lambda d$ and $\Lambda t$ pairs from the stopped $K^-$ reaction on $^4$He had been investigated, thereby $\Lambda d$ and $\Lambda t$ branches of non-mesonic three- and four-nucleon absorption processes of antikaon at rest were identified as well-separable processes, respectively. The branching ratio of the three-nucleon process, ($^4$He-$K^-$)$_{atomic} \rightarrow \Lambda d "n"$, is estimated to be $(0.9 \pm 0.1 (stat) \pm 0.2 (syst)) \times 10^{-3}$ from the normalized $\Lambda d$ spectrum in a $\Lambda d n$ final state, while the fraction of the four-nucleon process, ($^4$He-$K^-$)$_{atomic} \rightarrow \Lambda t$, is obtained to be $(3.1 \pm 0.4 (stat) \pm 0.5 (syst)) \times 10^{-4}$ per stopped $K^-$.