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Two emulsion stacks, exposed to magnetically analysed enriched K−-meson beam of average momentum 430 MeV/c and 440 MeV/c from Bevatron, have been used to estimate the relative abundance and lifetime of K−-mesons. While following 103 m of track length, 48 decay-like events were observed. From the analysis of events with good geometry the following decay modes have been established: Kμ2Kπ2Kμ3Kπ3(τ′) and Kβ. No example of τ−-decay was found in the line scan sample, but the mode has been established from an area scan event. No knowledge of K+-decay modes, or of the mass of the primary particle was assumed in the analysis. The mean mass, obtained from the decay kinematics of Kμ2 and Kπ2 mode, is (965.8−21.5+16.5) me. The mass value fromτ−-decay mode is found to be (964.45±2.91) me. The percentages of various decay modes are as follows: Kμ2 (56.9±12.8), Kπ2 (33.4±8.7), Kμ3 (5.9±3.1), Kπ3(τ′) (2.7±2.8), Kβ3 (2.9±1.9) and τ−(0+2.0). The mean lifetime has been determined after detailed considerations of the contamination due to decaylike clean interactions, and losses due to missing secondaries. The mean lifetime is (1.27−0.23+0.36)·10−8 s.

Analysis 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.

An 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.

The anisotropy of the distribution in the angleθ, between the direction of emission of the positron and that of the μ-meson, has been measured in stripped emulsion stacks exposed to the cosmic radiation. Assuming a distribution of the form (1 +a cosθ) a value of − .081 ± .05 has been obtained for «a ». This result is compared with those obtained by other workers and the depolarizing effects of photographic emulsion are discussed.

An example of interaction of an identified Ξ−-hyperon at rest in nuclear emulsion, is reported. Two hypernuclei are produced at the capture star; one is unambiguously identified as4H-hypernucleus from its characteristic decay mode,4HΛ→4He + π−, the second one is most probably a4,5He-hypernucleus decaying in the non π−-mesic mode. The hyperon is produced in a disintegration caused by a K−-meson of momentum, 1.5 GeV/c. Additional evidence for the strangeness value of the hyperon is obtained from the analysis of the parent K−-star. A charged K-meson is emitted in the production process, which on the grounds of strangeness and energy balance in the reaction, indeed proves the strangeness — 2 of the hyperon.

Over two hundred examples of the decay in flight of positive heavy mesons produced at the Bevatron have been observed in the photographic emulsions, and from these the lifetime of the particles has been estimated. The lifetime averaged over all modes of decay is found to be 1.35−0.13+0.16 s. The effect of experimental biases is discussed, and the final result is compared with that of other authors.

A 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−+ Open image in new window → →Λ0+π, Σ+ Open image in new window →Λ0+ Open image in new window ; and (b), by radiative decay: Λ0→Λ0+γ, to be separately distinguished. In sample (a), the observed value of the quantityα\(\bar p\)=0.23±0.24, and ofNf/Nb=25/27, a result consistent with an isotropic distribution. For sample (b), the distribution is asymmetric,α\(\bar p\)=1.12±0.27 andNf/Nb=33/9. Thus Λ0-hyperons produced by radiative decay display longitudinal polarization, as expected. A scanning procedure has been adopted which eliminates any possible contribution of spurious fore-aft asymmetry due to scanning bias.

148 m of K+ track have been followed in an unbiassed way and 109 inelastic interactions with emulsion nuclei found. In addition 3 K+-proton scattering events have been found and numerous cases of elastic scattering from emulsion nuclei. The differential cross-section for the elastic scattering has been plotted for three energy intervals and the results compared with those predicted by the optical model for various nuclear well depths. The variation of cross-section with energy for the inelastic events is found to be consistent with isotropy if the Pauli Exclusion Principle is taken into account and the best fit for the experimental points is obtained for a repulsive potential well of 20 MeV. The inelastic events have been analysed on the basis of the statistical model of the nucleus and an attempt has also been made to obtain from the experimental data the angular distribution in the C.M. system of the K-nucleon cross-section. On any reasonable assumption this appears to be peaked backwards. These data also demand a repulsive potential of ~ 20 MeV. The value of the average K-nucleon cross-section within nuclear matter for meson energies between 40 and 120 MeV is 4 mb/nucleon; allowing for the events forbidden by the exclusion principle this implies a cross-section of 6 mb on a free nucleon. Taking Σp = 14 ± 3) mb, it follows that ΣD= (2 ± 2) mb. The ratio of charge exchange events to noncharge exchange events is 20 ± 07 — the value expected in the limit of a vanishingly small interaction in theT = 0 state.

A total of 3,480 K/sup -/-mesons were observed. Of these, 445 interact in flight, at a mean energy of 40 Mev and only their general characteristics were studied. Little difference was observed between the number of unstable charged particles ( SIGMA plus or minus -hyperons and pi plus or minus -mesons) in these interactions and those in the 3,035 interactions at rest. The 3,035 K/sup - /-interactions at rest were studied in detail. The results on those interactions in which pi -mesons are emitted are given. An estimate of the SIGMA -hyperon nuclear potential is based on the energy spectrum of pi -mesons emitted in the K/ sup -/-interactions in which the only charged particles emitted are a pi meson and a SIGMA -hyperon. A detailed examination of ihe angular distribution of 2- pronged events, and of the sign ratio of the pi -mesons, the prong distribution and energy release in all events led to an estimate of the probabilities of absorption of positive and negative SIGMA hyperons in the parent nucleus, and to a partition of the events between the various primary reactions. (auth)

Measurements have been carried out on theπ-meson secondaries arising from the decay of positive π-mesons recorded in a stack of nuclear emulsions which had been exposed to the positive K-meson beam of the Berkeley « bevatron ». The distribution in energy of these secondaries is shown to be consistent with the view that the Τ-meson is a pseudo-scalar particle and they appear to exclude the possibility that the spin and parity of the particle are I-, 1+, 2+ or 3-.

The emission of Σ-hyperons from 3 037 K− capture stars at rest in nuclear emulsion has been studied. The identification of the hyperons is discussed. Charged Σ-hyperons are emitted from (17.6±1.0)% of all K−-stars while (9.6±0.6)% of them lead to the emission of both Σ-hyperons and π-mesons. The Σ−/Σ+ ratio for all stars is 0.86±0.12 while for stars in which a π-meson is also emitted it is 0.45±0.10. The difference between this latter value and the markedly different value (2.0) obtained for K−-interactions at rest in a hydrogen bubble chamber is attributed to the Fermi motion of nucleons in the nucleus, and a dependence of the relative K− transition amplitudes on the energy of relative motion of the K−-meson and nucleon. The branching ratio,R, of the number of Σ+ decays to π+ and proton respectively is 1.23±0.27. The stable prong distribution of the stars in which a hyperon is emitted, as well as the energy distribution of the Σ-hyperons at emission has been studied. About 16% of all identified charged Σ-hyperons had an emission energy above 60 MeV, and had to be attributed to multi-nucleon interactions of the K−-meson. It is estimated that the proportion of all multi-nucleon primary capture prccesses may be as high as (30÷40)%. The interaction of a K−-meson with a pair of neutrons seems to occur rarely, if at all. From the fraction of Σ+ emitting stars which also emit a π−-meson it is concluded that only about 10% of the π−-mesons fail to escape from the nucleus in which capture occurs. This could be understood if K−-capture occurs predominantly in the peripheral region of the nucleus. From a similar study of Σ− emitting stars it is found however that the proportion of π+ or π0-mesons, or both, that are absorbed in the nucleus is much higher. Estimates are made of the mean free path in nuclear matter of Σ-hyperons and π0-mesons. Most of the one-nucleon interactions leading to Σ-hyperon production take place with protons and the transition amplitudes corresponding to theT=1 state of isotopic spin is smaller than theT=0 transition amplitude.

The decay modes of K+-mesons which have been inelastically scattered from nuclei in emulsion have been determined and. it is shown that their relative frequencies are consistent with those obtained for K+-mesons which have not undergone nuclear interaction. Measurements were also made on a total of 286 decay events with a singly charged secondary with the object of discovering without detection bias, particles decaying in the rare τ’ and the Kμ3 modes.

On the basis of recent experience, it is suggested that Ilford G-5 emulsion stacks should be refrigerated after exposure when they are to be shipped over large distances by public transport.