ln an attempt to establish the existence of a neutral cascade hyperon /sup 0/, the 15-inch hydrogen bubble chamber was operated in a separated beam of 1.15 sintering time 0.02-Bev/c K- mesons produccd by the Bevatron. Of seven double V/sup 0/ events one was interpreted as a /sup 0/ cascade. A photograph and diagrams are presented. (W.D.M.)

/pdf/neutral-cascade-hyperon-event-47pxjka2xd.pdf

Neutral Cascade Hyperon Event

In this paper we present some results on charged heavy mesons. They were obtained with an experimental arrangement consisting essentially of two large cloud-chambers placed one above the other. The top chamber had a magnetic field while the bottom chamber was of the multiplate type. The contents of the different sections of the paper can be summarized as follows: 1. The double cloud-chamber method is compared with other more conventional methods. 2. The apparatus is briefly described. 3. The behaviour in the multiplate chamber of the charged secondaries of V±-decays occurring in the top chamber is disscussed. π-mesons have been identified through their nuclear interactions. The presence of μ-mesons is also strongly suggested by:a) the long mean free path of the secondaries andb) one direct mass measurement. 4. S and slow V±-events observed in the multiplate chamber are discussed. It is shown that one should distinguish between two groups of decays: One with secondaries of range smaller than 20 g cm−2 of Pb, the other with larger range secondaries. Although the first group can be due to τ-mesons, the second group cannot be so explained, at least not phenomenologically. 5. The results of mass measurements—from range and momentum—on the primaries of the second group of events are presented. The measurements agree with a unique value of (914±20) me; which appears to be different from the τ-mass. 6. We show that some, and probably most, of the secondaries of this second group of events are μ-mesons. This conclusion is based on the dynamics of the decay and results from the measured mass of the primary particle and the observed ranges of the secondaries. The observation of one large angle scattering indicates, however, that τ-mesons may also be present among the secondaries.

Étude des mésons K chargés, au moyen de deux chambres de Wilson superposées

Two cosmic-ray decay events have been photographed in a cloud chamber under conditions that yield mass values from combined magnetic-field momentum measurements and ionization measurements from droplet counting. A method has been developed for assigning meaningful probable errors to the ionization measurements. The first event is interpreted as the decay of a neutral $V$ particle into a positive $\ensuremath{\pi}$ meson and a negative particle of mass $1850\ifmmode\pm\else\textpm\fi{}250{m}_{e}$. On the assumption of a two-body decay, the $Q$ value for the decay is 11.7\ifmmode\pm\else\textpm\fi{}4 Mev. The second event is a cascade decay that can be summarized by the following reaction: ${{Y}^{\ensuremath{-}}\ensuremath{\rightarrow}67\ifmmode\pm\else\textpm\fi{}12 \mathrm{Mev}+{\ensuremath{\pi}}^{\ensuremath{-}}+{\ensuremath{\Lambda}}^{0}}{\ensuremath{\searrow}}{40\ifmmode\pm\else\textpm\fi{}13 \mathrm{Mev}+{\ensuremath{\pi}}^{\ensuremath{-}}+p.}$ The proton of the ${\ensuremath{\Lambda}}^{0}$ decay is identified by a measured mass of $2050\ifmmode\pm\else\textpm\fi{}350{m}_{e}$. On the assumption of a twobody decay, the mass of the primary $V$ particle is $2600\ifmmode\pm\else\textpm\fi{}34{m}_{e}$.

A V -Decay Event with a Heavy Negative Secondary, and Identification of the Secondary V -Decay Event in a Cascade

In a series of pictures taken with a multiplate cloud chamber, we have observed a number of charged unstable particles considerably heavier than $\ensuremath{\pi}$-mesons, of which some decay at rest ($S$ particles) and some decay in flight (${V}^{\ifmmode\pm\else\textpm\fi{}}$ particles). In each case the charged decay product is a particle of mesonic mass. From our results, which are not yet completely conclusive, it appears that most of the observed events can be explained by the two-body decay of a single kind of particle. The evidence concerning the mass of this particle, its mean life, and the nature of the neutral decay product is discussed. Our observations are compared with those of other experiments.

Cloud-Chamber Observations of the Heavy Charged Unstable Particles in Cosmic Rays

A number of independent accurate measurements of the masses of light mesons are critically reviewed. Assuming the positive-and negative-charged mesons to have equal masses, best values for the pion and muon masses can be calculated. It is found that the negative π- and μ-mesic X-ray energies measured by K absorption edges can be combined with the mass difference between the positive pion and muon to give a result with a standard deviation approximately one third of the assigned errors of the best previous measurement. All the results are in satisfactory agreement and can be combined in the usual way. The mass results are as follows:Mμ=(206.86±0.11) me;Mπ==(273.27±0.11) me. Experimental data on the mean lives, spins, parities, and decay modes are also reviewed and the results are given. The measurements of the masses of the various K-mesons are obtained in several ways:MKπ2=(966.0±1.5) me;MKπ2=(965.3±1.9) me;MΣ=(966.8±0.4) me. There is at present no evidence for a difference in the masses to a precision of 1 ÷ 2 me. Results on the Σ+-Σ− and τ+ masses and lifetimes and the analysis of τ+ decay are discussed. At present the experimental equality of these particles seems to be contradictory to assigning a spin of less than 2. The cosmic-ray data on the ϑ0 lifetime are reviewed and recent results on artificially-produced ϑ0’s are discussed. The hyperon mass data are reviewed.MΔδ=(2181.74±0.35) me;MΣδ=(2 327.4±1.0) me. The latest data on a Σ+ − Σ− mass difference and their mean lives are presented.

The masses of light mesons, K-mesons and hypersons in 1956

Twenty-one examples of the decay of charged V-particles have been found among 25 000 counter-controlled cloud-chamber photographs obtained on the Pic-du-Midi (2 867 m). These events have been analysed and compared with the data obtained by other groups. The measurements show that, if the majority of the V ±-tracks are produced by one type of particle having a single mode of decay, there must be at least two neutral secondary particles, in addition to the charged secondary particle. The latter is probably a μ- or a π-meson and the combined mass of the neutral particles must be less than 1 000 me . Since the κ-particles, of mass about 1 200 me , which were discovered in photographic emulsions, also decay into a charged meson and at least two neutral particles, it is plausible to assume, provisionally, that the V± -particles and the κ-particles are the same. On this assumption most of the available data concerning V± - and κ-particles can be explained if the unstable particle has a mass of about 1 2...

LVI. The properties of charged V-particles

Data for the determination of the mean lifetime of charged V-particles are discussed, following the procedure outlined by Wilson and Butler (1952). The tracks of twenty-seven V ±-particles have now been photographed on the Pic-du-Midi (2 867 m) by Armenteros et al. (1952) and by the authors in a circular cloud chamber, 28 cm in diameter. It is shown that, using these data, the chamber is too small for the lifetime to be determined, but a lower limit of 1·0 × 10-10 sec is obtained. Furthermore, the relation between the frequency of production of energetic V ±-particles in penetrating showers of average energy (10–30) Bev, and various assumed lifetimes is discussed. Using recent photographic emulsion data on the frequency of particles of mass about 1200 me in the same type of penetrating shower an upper limit for the lifetime of 10-8 sec is obtained.

CXIX. The mean lifetime and frequency of production of charged V-particles

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LVI. The properties of charged V-particles

CXIX. The mean lifetime and frequency of production of charged V-particles