Decay In Flight Research Articles

Example ofτ+-Decay in Flight

A ${\ensuremath{\tau}}^{+}$-meson, of 0.83 Bev/c, is observed to undergo normal decay in flight with $Q(3\ensuremath{\pi})=73.9\ifmmode\pm\else\textpm\fi{}5.8$ Mev. The center-of-mass kinetic energies are found to be ${T}^{\ensuremath{'}}=24.3\ifmmode\pm\else\textpm\fi{}1.8 \mathrm{and} 28.7\ifmmode\pm\else\textpm\fi{}1.8$ Mev for the two positive pions and ${T}^{\ensuremath{'}}=20.9\ifmmode\pm\else\textpm\fi{}4.3$ Mev for the negative pion.

Hyperon events in photographic emulsions

Details are given of six hyperon events observed in photographic emulsions. Two of these decay at rest into protons and giveQ-values of 115.8±1.0 MeV and 113.5±1.7 MeV for the assumed decay scheme: Y+ → p+π0+Q. Three others decay in flight; two giveQ-values 115±7 MeV and 103±10.5 MeV for the decay mode: Y± → n+π±+Q; the third is in agreement with the cascade type of decay: Y− → A0+π−+Q and has aQ=59±11 MeV. The sixth event has been interpreted as the interaction at rest of a negative hyperon; from the parent star of this hyperon there also emerges a K-meson.

A possible example of the decay in flight of a θo

A possible example of the decay in flight of a θo

LXI. On the mass of the Λ0-particle

Summary In a stack of stripped photographic emulsions, twenty events of type 2+0 n have been observed, in each of which the outgoing particles are a proton and a negative π-meson respectively; the latter particle was identified by the characteristic star it produced when brought to rest in the emulsion. Assuming that each of these events represents the decay in flight of a neutral hyperon according to the scheme Λ 0→π -+P+Q, values of the energy release Q have been calculated. In eleven of the events the proton could be traced to the end of its range; the energies of both particles could then be deduced using appropriate range-energy relations. In the remaining nine examples, the energy of the proton was deduced from grain density considerations and was accordingly less well determined.

L. Some observations on the decay of neutral V-particles in photographic emulsions

Summary In an examination of two-particle events recorded in photographic emulsions, four examples have been observed of a type similar to the decay of Λ 0-particles in Wilson chambers. In three of them, the measured energy-release in the decay is ∼40 mev; in the fourth example it is ∼70mev. An event has also been observed, which appears to correspond to the decay in flight of a ϑ 0-particle, emitted from a nuclear disintegration of type 10+f 7p. One of the secondary particles arising from the decay is a negative π-meson. The measured Q value is 202±11 mev.

S -particles and charged V -particles

A detailed discussion is given of the known properties of the unstable S -particles and charged V -particles, other than their lifetimes. S -particles are singly charged and decay at rest in thin lead plates inside a cloud chamber into one charged secondary particle and one or more neutral particles. Charged V -particles are also singly charged and decay in flight in the cloud-chamber gas into a charged secondary particle and one or more neutral particles. Some of the S -particles are probably identical with the X -particle, and the charged V -particles probably consist of a mixture of K - and χ -particles.

III. Analysis of V-events

Abstract From the observed momenta and angles of decays in flight, variables are constructed which are better suited for the analysis than the measured quantities themselves. These variables are 1/P, the reciprocal of the primary momentum, α, a combination of the longitudinal momenta of the secondaries, and either pt , the transverse momentum, or the quantity e=2pt/P. The regularities in the distribution of the new variables, to be expected from a two-body decay, are discussed. The decay scheme may be derived by comparison with the experimental distributions.

Unusualπ−μDecays in Photographic Emulsions

A total of 11 841 $\ensuremath{\pi}\ensuremath{-}\ensuremath{\mu}$ decays has been studied in Ilford C-2 and G-5 photographic plates, where both the $\ensuremath{\pi}$- and $\ensuremath{\mu}$-meson tracks stopped in the emulsion. In 12 cases the range of the $\ensuremath{\mu}$-meson track from the $\ensuremath{\pi}$-meson decay is less than 480 microns and in 2 cases the range is greater than 720 microns. The ranges of the $\ensuremath{\mu}$-meson tracks of the 14 unusual $\ensuremath{\pi}\ensuremath{-}\ensuremath{\mu}$ decays are: 120, 185, 258, 260, 290, 416, 430, 441, 444, 470, 470, 476, 828, and 1035 microns. The normal range of the $\ensuremath{\mu}$-meson from $\ensuremath{\pi}$-meson decays is about 600 microns. A study of the grain density in C-2 plates, gap density in G-5 plates, and the number and energy of the $\ensuremath{\delta}$-rays along the short $\ensuremath{\mu}$-meson tracks indicates that the $\ensuremath{\mu}$-mesons were ejected from the $\ensuremath{\pi}$-decays with a lower velocity than from normal $\ensuremath{\pi}\ensuremath{-}\ensuremath{\mu}$ decays. It is possible to explain the short range of the $\ensuremath{\mu}$-meson in 4 of the events and the long range of the $\ensuremath{\mu}$-meson in the 2 events by assuming that the $\ensuremath{\pi}$-meson decayed in flight. The grain density or gap density along the $\ensuremath{\mu}$- and $\ensuremath{\pi}$-meson tracks in the remaining 8 events is inconsistent with the assumption that the short range of the $\ensuremath{\mu}$-meson is due to the decay in flight of the $\ensuremath{\pi}$-meson. If a correction is made for the thickness of the emulsion, the probability that a $\ensuremath{\mu}$-meson from a stopped $\ensuremath{\pi}$-meson decay will have a range less than 480 microns is found to be 3.3\ifmmode\pm\else\textpm\fi{}1.3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$. This probability is in general agreement with theoretical predictions based upon the assumption that a soft photon is occasionally emitted from the $\ensuremath{\pi}\ensuremath{-}\ensuremath{\mu}$ decay resulting from the charge acceleration of the $\ensuremath{\mu}$-meson.

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

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.

Range Distribution ofμ-Mesons fromπ-Meson Decay in Photographic Emulsion

The lengths of $\ensuremath{\mu}$-meson tracks from 1000 $\ensuremath{\pi}$-meson decays have been measured in two Ilford C-2 200-micron thick emulsions, which had been exposed by R. Sagane in a spiral orbit spectrometer to the Berkeley cyclotron. Shrinkage factors obtained from this analysis were used to calculate the true ranges of the $\ensuremath{\mu}$-meson tracks. The distribution of true ranges meets statistical tests for a Gaussian distribution; it has a mean of 597\ifmmode\pm\else\textpm\fi{}1 microns and a standard deviation of 29.1\ifmmode\pm\else\textpm\fi{}0.7 microns. Since decay in flight and soft photon emission accompanying decay have negligible effects in this study, the straggling parameter for 4.1 Mev $\ensuremath{\mu}$-mesons in photographic emulsion can be obtained; it is 4.86\ifmmode\pm\else\textpm\fi{}0.12 percent. The effect of experimental uncertainties on these values can be about 0.1 percent, which is slightly less than the statistical limits imposed by the finite number of events.

The Occurrence of Heavy Mesons in Penetrating Showers

In the course of a cloud chamber study of penetrating showers, two events have been observed which probably represent the decay in flight of τ-mesons,(1) and one event which probably represents the decay in flight of a K-meson.(2)