J. Zakrzewski

The identification of a double hyperfragment

Abstract The detailed analysis is presented of an event which is interpreted as the mesonic cascade decay of a double hyperfragment produced by the capture of a Ξ− hyperon on a light emulsion nucleus. The most likely interpretations of the double hyperfragment are those in terms of either ΛΛBe10 or ΛΛBe11.

A new determination of the binding-energy values of the light hypernuclei (A ⩽ 15)

Abstract A new determination of the binding-energy values of the light hypernuclei ( A ⩽ 15) is reported, based on the analysis of some 27 000 π − mesonically-decaying hypernuclei produced by stopping K − mesons in nuclear emulsion. The results are combined with previous data obtained using similar experimental and analysis procedures.

Some properties of the charged Σ hyperons

Abstract A sample of some 7500 K − meson captures at rest on hydrogen in emulsion giving rise to charged Σπ pairs has been used to determine r , the decay branching ratio of the Σ + hyperon, λ, the ratio of Σ − to Σ + hyperon production, τ Σ − , the lifetime of the Σ − hyperon, and C , the mean orbital capture time of Σ − hyperons in emulsion. The results obtained are r= σ + → n +π + all σ + decay modes = 0.484 ± 0.015, γ = σ − π + σ + π − = 2.34 ± 0.08, γ σ − = 1.41 +0.09 −0.08 × 10 −12 sec , and C 10 −12 sec.

The decay of heavy hypernuclei

In a sample of 38238 interactions found in photographic emulsions exposed to K− mesons of 1.3 and 1.5 GeV/c momenta, a total of 1385 heavy hypernuclei (40 < A < 100) were observed, of which 11 decayed mesonically. The following results were obtained: an upper limit of 27±3 MeV for the Λ0 nuclear potential well depth, a value of Q− in the range 100 to 200 and a fraction, n, in the range 0.6 to 0.9 of non-mesonic decays stimulated by the weak Λ0-neutron interaction.

Confirmation of the existence of a particle-unstable state of the Λ12C hypernucleus

Abstract A study has been made of the K− meson absorptions at rest in emulsion nuclei of the type K− + nucleus → π− + charged particle + hypernucleus. The existence of the particle unstable resonant state of the Λ12C hypernucleus, decaying via Λ 12 C → 1 H + Λ 11 B , has been firmly established. The excitation energy and natural width of this state are about 11 MeV and 0.4 MeV respectively.

Production of hyperfragments from the interactions of 1.3 GeV/c and 1.5 GeV/c K− mesons with emulsion nuclei

Study of particle interactions in emulsion stacks exposed to 1.3 and 1.5 Bev/c K/sup -/ meson beams gives support to the idea that hyperfragments of range less than 10 mu m are residual spallation products containing trapped LAMBDA / sup o/ hyperons resulting from K/sup -/ interactions in emulsion nuclei. (D.C.W.)

Evidence for the existence of particle-unstable states of the Λ12C and Λ14N hypernuclei

Abstract Evidence is presented for the existence of particle-unstable states of the Λ12C and Λ14N hypernuclei produced by the absorption at rest of K− mesons in light emulsion nuclei.

On the binding energy values and excited states of some A>=10 hypernuclei

Abstract New binding energy values for the hypernuclei 10ΛBe and 14ΛC have been determined while those of 13ΛC and 15ΛN have been reassessed. The existence of a narrow particle-unstable state of 12gLC is affirmed but the previously quoted evidence for the existence of a narrow state of the 14ΛN hypernucleus is shown to be invalid.

Production of hyperfragments from the interactions of 3.0 GeV/c and 5.0 GeV/c K− mesons with emulsion nuclei

SummaryA study has been made of the production of hyperfragments by the interactions of K−-mesons of 3.0 and 5.0 GeV/c momentum in nuclear emulsion. The observed frequencies of production, (3.0±0.1)% and (2.2±0.1)% respectively, are significantly smaller than at lower K−-meson momenta, while the range distributions show a relative increase in the number of hyperfragments of range greater than 5 µm. This increase is attributed to a larger contribution from the fragmentation process, which is especially significant at intermediate ranges [(10÷50) µm], and to greater mean ranges for the heavy hyperfragments, which broaden the peak at short ranges (⩽10 µm). The hyperfragments of range less than 10 µm are mainly heavy residual products of silver and bromine nuclei; their mass numbers differ on the average from those of the parent nuclei by about 30 and 35 nucleon masses for 3.0 and 5.0 GeV/c interactions respectively. Eight examples of π− mesonic decays of heavy hyperfragments, and one probable example of a double hyperfragment, have been observed.RiassuntoSi è studiata la produzione di iperframmenti nelle interazioni di mesoni K− con impulso di 3.0 e 5.0 GeV/c in emulsioni nucleari. Le frequenze di produzione osservate, rispettivamente (3.0±0.1)% e (2.2±0.1)%, sono significativamente minori che a impulsi inferiori del mesone K−, mentre le distribuzioni dei percorsi mostrano un relativo aumento del numero di iperframmenti di percorso maggiore di 5 µm. Si attribuisce questo aumento ad un maggiore contributo del processo di frammentazione, che è particolarmente significativo per percorsi intermedi [(10÷50) µm], e ai maggiori percorsi medi degli iperframmenti pesanti, che allargano il picco a percorsi brevi (⩽10µm). Gli iperframmenti con percorso inferiore a 10 µm sono principalmente residui pesanti dei nuclei di argento e bromo; i loro numeri di massa differiscono in media da quelli dei nuclei genitori di circa 30 e 35 masse nucleoniche rispettivamente per le interazioni di 3.0 e 5.0 GeV/c. Si sono osservati otto esempi di decadimenti π− mesonici degli iperframmenti pesanti ed un probabile esempio di doppio iperframmento.

The identified ΛΛ-hypernuclei and the predicted H-particle

The existence of the H particle, the dihyperon predicted by Jaffe, would bring into question the existence of double hypernuclei. We review the two double hypernucleus events published in the literature. We include an independent report, hitherto unpublished, which was made on the ΛΛ10Be event in 1963 and clarifies the salient features of the event; this report reaffirms its published interpretation. We have made a simple calculation of the energy spectrum for Ξ- hyperons produced with K- beams in past emulsion experiments, with a result which accounts adequately for the paucity of reported double hypernucleus events. We outline a hybrid emulsion experiment that would locate Ξ- hyperon interactions efficiently and could thereby greatly improve our knowledge of double hypernuclei.