Search

A double-hyperfragment event has been found in a hybrid-emulsion experiment. It is identified uniquely as the sequential decay of ( 6)(LambdaLambda)He emitted from a Xi(-) hyperon nuclear capture at rest. The mass of ( 6)(LambdaLambda)He and the Lambda-Lambda interaction energy DeltaB(LambdaLambda) have been measured for the first time devoid of the ambiguities due to the possibilities of excited states. The value of DeltaB(LambdaLambda) is 1.01+/-0.20(+0.18)(-0.11) MeV. This demonstrates that the Lambda-Lambda interaction is weakly attractive.

Results are presented of a bubble chamber study of K−-meson interactions at rest in helium leading to the Λπ−pd final state. It is found that (75±1)% of this final state results from the two-step mechanism of internal Σ-Λ conversion via processes such as\(K^ - {\mathcal{N}} \to \Sigma \pi \) followed by\(\Sigma {\mathcal{N}} \to \Lambda {\mathcal{N}}\). The experimental results are compared to the predictions of a double-impulse model, in which a contribution has been included from a Σ-Λ conversion process involving two nucleons in order to reproduce the baryon momentum spectra. The model is capable of explaining the features of the invariant-mass distributions of the finalstate particles without invoking resonance production.

A study has been made of K--meson interactions at rest in the CERN 1.1 m3 heavy-liquid bubble chamber filled with a mixture of hydrocarbons. The emission frequency of Λ0-hyperons following K--meson absorptions in carbon nuclei is determined to be 0.68 ± 0.02. A detailed study of the (Λ0π-) final state has allowed an estimate to be made of the internal-conversion probability C(Σ+) of {perspective}+-hyperons produced in association with π--mesons. The result is C(Σ+)=0.62 ± 0.02. The contribution of the direct channel to the (Λ0π-) final state is found to be 0.23 ± 0.01. The results are compared with those obtained for other absorbing media. © 1977 Societa Italiana di Fisica.

The mean cascade times of both K−-mesons and Σ−-hyperons in their captures at rest in liquid helium have been determined to be (3.1±0.4) · 10−10 s and less than 3.6 · 10−11 s (with a confidence level of 90%) respectively. The finding of a much lower mean cascade time for Σ−-hyperons than for K−-mesons lends weight to the hypothesis of trapping of negative hadrons in metastable orbits in helium.

A study has been made of K − meson interactions at rest in the CERN 1.1 m 3 heavy liquid bubble chamber filled with a mixture of hydrocarbons. The data are used to determine (i) the internal conversion probability, C ( Σ − ), of Σ − hyperons produced in association with π + mesons by K − meson interactions in carbon nuclei, (ii) the relative emission frequencies of ( Σ + π − ) and ( Σ − π + ) pairs, E ( Σ + π − / Σ − π + ), and the emission frequency E ( Σ ± π ∓ /K − ), of ( Σ ± π ∓ ) pairs per K − meson absorption in carbon, (iii) the branching fraction, P ( Σ − π + /K − ), for the primary process K − + p → Σ − + π + in carbon and (iv) the trapping probability, T ( Λ °), for Λ ° hyperons produced by Σ − hyperon interactions in carbon nuclei. The results are: C ( Σ − ) = 0.38 ± 0.03, E ( Σ + π − / gS − π + ) = 1.25 +- 0.09, E ( Σ ± π −+ /K − ) = 0.164 ± 0.006, P ( Σ − π + /K − ) = 0.127 ± 0.004 and T ( Λ °) = 0.13 ± 0.04, where the errors quoted are statistical and correspond to one standard deviation. Possible systematic errors were estimated to be at most of the same order of magnitude as the statistical uncertainties.