D.P. Goyal

Charm production in 400 GeV/c proton-emulsion interactions

Abstract 5032 proton-emulsion interactions at 400 GeV/ c momentum have been carefully scrutinized for production and decay of charged charm particles. In order to detect these decays, shower tracks from 3056 stars have been followed to a maximum length of 1 mm and those from 1976 stars up to 2 mm. A total of 23 three-prong charm-like candidates have been recorded in the forward cone. The background due to γ-overlap on a shower track, trident/pseudo-trident production and secondary interactions is estimated to be 15. Attributing the signal of 8 events to Λ c + and assuming the branching ratio of Λ c + → 3 prong to be 0.6 and τ Λ c to be 10 −13 sec we obtain the production cross section to be 106±39 μ b/nucleon. Out of these 8 events one example of semileptonic decay of Λ c + is seen.

The stimulated decay of the Λ-hyperon

The relative strengths of proton stimulation ( LAMBDA -p) and neutron stimulation ( LAMBDA -n) non-mesonic decay interactions of A-hypernuclei were investigated by examining 19 observed examples of He-hyperfragments decaying in the non-mesic mode. The ( LAMBDA -p) interaction was observed to predominate over the (A-n) interaction by a ratio of 3.8 to 1, in excellent agreement with the expected ratio of 4 to 1. (H.D.R.)

The mass of the A0-hyperon

SummaryAn accurate determination of the A0-mass has been made using nuclear emulsion. From an analysis of 101 A0-decays, we obtain for the mass of the A0-hyperon, MA= (1115.46± 0.15) MeV andQA = (37.62± 0.14) MeV.RiassuntoAbbiamo eseguito un’accurata determinazione della massa del A0, usando emulsioni nucleari. Dall’analisi di 101 decadimenti A0 otteniamo per la massa dellïperone A0: MA=(1115.46±0.15) MeV e QA = (37.62±0.14) MeV.

Non-mesic decay of hypernuclei

A systematic study of hypernuclei, produced by K− and Σ− interactions in nuclear emulsion, and decaying in the non-mesic mode, is reported. The contaminations from the various background phenomena have been estimated and the sample is found to be reasonably pure. From the energy distribution of the decay products, a clear separation between the proton- stimulated and neutron-stimulated events has been obtained. The ratios of the proton to neutron stimulated decays for He-hyperfragments and for hyperfragments with charge ≥3 are determined as 3.8 and 2.5, respectively. These values are clearly greater than unity, and according to Ferrari and Fondas calculations, therefore, indicate that the stimulation process occurs predominantly when the hyperon is in the Λ-state. A model of the stimulation process is proposed. The non-mesic/mesic ratio Q as a function of the hyperfragment-charge is determined. The weighted mean Q (ΛHe) of the various emulsion works is obtained as 1.48±0.23. From this, the ratio |p|/|s| of the p and s channel amplitudes in Λ-decay is estimated to be 0.20−0.05+0.04.

Binding energies of the Λ0-hyperon in hypernuclei

Abstract An analysis of 29 hypernuclei produced by the interactions of K - -mesons and Σ - -hyperons in nuclear emulsion and decaying in the π - -mesic mode, is presented. Binding energies of the Λ 0 -hyperon in the hypernuclei Λ H 4 (6 events), Λ He 4 (4 events), Λ He 5 (9 events) and ΛLi 9 (1 event) are obtained as (2.37±0.30) MeV, (2.27±0.27) MeV, (3.27 ± 0.18) MeV and (7.75±0.80) MeV, respectively. The binding energies are derived from the Q Λ value determined in the same emulsion stack from which the hyperfragment data also originated. This makes the systematic errors in the binding energies negligible; the errors quoted are therefore only statistical. Besides the most commonly occuring decay mode of Λ He 5 , the rare decay mode Λ He 5 → He 3 +H 2 + π - has also been observed.

Λp mass enhancement in the reactionK−d→Λpπ−π0

Abstract An enhancement in the Λp mass distribution from the analysis of bubble chamber data of the reaction K−d → Λpπ−π0 at Ks− momenta of 1.45 and 1.65 GeV/c is reported. The distribution is fitted to a Breit-Wigner resonant structure plus phase-space background. The best fit to the data gives the value of the peak at ⋍2115 MeV and the width of the distribution ⋍150 MeV . A comparison of this result with those obtained by other groups suggests that the enhancement is most likely due to a non-resonant effect.

Interactions of negative K-mesons in nuclear emulsion at energies (0÷180) MeV

SummaryAnalysis of 384 K−-meson interactions in flight with complex nuclei of the emulsion obtained by following 102.93 meters of K− track length, is presented. The average mean free path in the energy interval (30÷180) MeV is found to be (26.82±1.39) cm. The variation of the interaction mean free path with K− energy is discussed. A study of K− inelastic scattering from emulsion nuclei has been made and it is concluded that the nuclear potential for K−-mesons is strongly attractive. The energy spectra of charged pions and hyperons emitted from K− interactions at these energies are discussed. It is shown that with increasing energy of the K−-meson the fractions, π−/π+ and Σ−/Σ+, also increase. The rates for various K−-single nucleon reactions have been determined. A comparison of these rates at different K− energies shows an enhancement in the direct Λ0 production.RiassuntoSi presenta l’analisi di 384 interazioni in volo di mesoni K− con i nuclei complessi dell’emulsione, ottenute seguendo 102.93 metri di lunghezza di tracce di K−. Si trova che il cammino libero medio nell’intervallo di energie (30÷180) MeV è in media (26.82±1.39) cm. Si discute la variazione del cammino libero medio di interazione con l’energia dei K−. Si è eseguito uno studio dello scattering inelastico dei K− da parte dei nuclei dell’emulsione e si conclude che il potenziale nucleare dei mesoni K− è fortemente attrattivo. Si discutono gli spettri di energia dei pioni carichi e degli iperoni emessi dalle interazioni di K− di tali energie. Si dimostra che al crescere dell’energia del mesone K− crescono anche le frazioni π−/π+ e Σ−/Σ+. Si sono determinate le proporzioni delle varie reazioni K−-nucleone singolo. Un confronto di queste proporzioni a differenti energie dei K− mostra un esaltamento della produzione diretta di Λ0.

Concerning fore-aft asymmetry in Λ0-decay

SummaryA sample of Λ0-hyperons recorded in photographic emulsions has been identified by estimating the energy release,Q, in their decay. The observations have then been used to study fore-aft asymmetry in the decay of the Λ0-hyperon. The energy spectrum of Λ0-hyperons has allowed the fractions produced (a), by strong interactions: K−+→ →Λ0+π, Σ+→Λ0+; and (b), by radiative decay: Λ0→Λ0+γ, to be separately distinguished. In sample (a), the observed value of the quantityα

Study of R/sub 3/- relationship from 400-GeV p-nucleus interactions

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