M. W. Friedlander

Hyperon events in photographic emulsions

SummaryDetails 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.RiassuntoSi descrivono in dettaglio sei iperoni osservati in emulsioni fotografiche. Due di di essi decadono a riposo in protoni e danno perQ valori di 115,8 ± 1,0 MeV e 113,5±1,7 MeV per il presunto schema di decadimento Y+ → p+π0+Q. Tre altri decadono in volo: due danno perQ valori di 115±7 MeV e 103±10,5 MeV per lo schema di decadimento Y± → n+π±+Q: il terzo si accorda col tipo di decadimento in cascata: Y− → A0+π−+Q e ha unQ=59±11 MeV. Il sesto evento è stato interpretato come l’interazione a riposo di un iperone negativo; dalla stella da cui origina questo iperone emerge anche un mesone K.

CXV. Evidence for the β-decay of a K-meson

Summary The decay at rest of a K-meson in which the secondary particle appears to be an electron of ∼90mev has recently been observed. The secondary particle, after traversing a distance of 2·3 cm in the emulsion, appears to have been sharply deviated; thereafter, the track is closely similar to that of a slow electron. The grain density in the track, before and after the deviation, is indistinguishable from the ‘plateau value’. The most plausible explanation of this behaviour is that it is due to the sudden loss of energy of an electron through the production of bremsstrahlung. Alternatively, the secondary particle could be assumed to be (a) a π-meson which interacts with a nucleus and undergoes change exchange, the product nucleus subsequently suffering β-decay, or (b) a μ-meson which decays in flight. The last two possibilities have been considered and appear very improbable.

Some aspects of the nuclear capture of hyperons and K-mesons

SummarySome predictions are made concerning the characteristics of the interactions produced by the nuclear capture of K−- and Y−-particles. It is assumed that the capture reaction is the inverse of the «associated production mechanism». A comparison is made between these predictions and the experimental data. The significant conclusions are: (i) the capture process sometimes involves two or more nucleons rather than a single nucleon; (ii) in view of the possible existence of Σ0-particles and their rapid transformation to Λ0-particles, the observation of Λ0-particles as end products of a capture process does not necessarily indicate that they were produced in the initial reaction; (iii) there appears to be an absence of μ-mesons of ∼ 120 MeV; this might indicate the production of a Σ0-particle instead of a Λ0-particle in the initial reaction or that the capture involves two or more nucleons; (iv) the available observations on capture stars are consistent with the general features of the theory of Gell-Mann and Pais.RiassuntoSi fanno alcune previsioni riguardanti le caratteristiche delle interazioni prodotte dalla cattura nucleare di particelle K− e Y−. Si assume che la reazione di cattura sia l’inversa del «meccanismo delle produzioni associate». Si istituisce un confronto tra queste previsioni e i dati sperimentali. Le conclusioni di rilievo sono: (i) il processo di cattura coinvolge a volte due o più nucleoni anzichè uno solo; (ii) in vista della possible esistenza di particelle Σ0 e della loro rapida trasformazione in particelle Λ0, l’osservazione di particelle Λ0 quali prodotti finali di un processo di cattura non è necessariamente un indice che esse sono state prodotte nella reazione iniziale; (iii) si constata l’assenza di mesoni μ di ∼ 120 MeV; questo potrebbe essere un indice della produzione nella reazione iniziale di una particella Σ0 invece di una Λ0, o che la cattura coinvolge due o più nucleoni; (iv) le osservazioni di stelle di cattura note sono in accordo con le linee generali della teoria di Gell-Mann e Pais.

The production of a pair of heavy mesons in a high-energy nuclear interaction

Recent ly there have been reported several examples of nuclear interact ions in which occur the associated production of a hyperon and a heavy meson; in those examples where an identificat.ion of the charge of the heavy meson has been possible it has always been shown to be posi t ive or neutral . In this communica t ion we describe an even t in which a negative K-mesm,, K (Brd), is produced in association with a~+other heavy meson. The nega | ive K-meson capture s tar was found in the course of scanning in photographic emulsion. The t rack of tim incoming part ic le was /:raced back to its origin which was foui~d to be a s tar of type 6 + 5p. The or ientat ions of the remaining t racks f rom the s tar were such that , wi th one except ion, reliable measurements could be made on all, and the i r na ture defined. The details and results of the measurements on the tracks are shown i~ Ta.ble l . The to ta l

LI. Observations on charged hyperons in photographic emulsions

Summary Two examples of charged hyperons have been observed in photographic emulsions. One decays in flight, and its transformation may be re-presented Y± → L± + N0 + Q, the release of energy, Q being consistent with values obtained in other laboratories. In the other example, the secondary is a fast proton. This event may represent either the decay of a new type of hyperon or the nuclear capture of a negative hyperon.

Parent stars of K+-mesons

SummaryA study has been made of the parent stars of K-mesons produced by the Cosmic Radiation. Emission angle and energy spectra are given for these mesons, together with a distribution of star sizes. An estimate is made of the frequency of occurrence of associated hyperons, other K-mesons and hyperfragments. Three particularly interesting events are described, including one which has enabled the mass of the negative Σ-hyperon to be calculated as 2 344±6 me.RiassuntoÈ stato compiuto uno studio su stelle madri di mesoni K+ prodotti dai raggi cosmici. Vengono dati spettri della energia e dell’angolo di emissione per i mesoni K+ e la distribuzione delle stelle. Viene valutata la frequenza di emissione di iperoni, ulteriori mesoni K+ e iperframmenti associati. Sono descritti tre eventi particolarmente interessanti, uno dei quali ha permesso di calcolare la massa dell’iperone Σ− in (2 344±6) me.

THE RANGE IN G5 NUCLEAR EMULSION OF PROTONS WITH ENERGIES 87, 118, AND 146 MEV

SummaryA comparison was made between the ranges of artificially accelerated protons in Aluminium and in Ilford G5 photographic emulsion. The ranges in emulsion were obtained by direct measurements along the particle tracks, and those in Aluminium by an attenuation method. The ranges of protons of three different energies were 19.31, 13.23 and 7.82 g/cm2 in Aluminium, and 22.85, 15.58 and 9.50 g/cm2 in emulsion of density 3.791 g/cm3 conditioned to 58% relative humidity. The corresponding energies were 146.5 MeV, 117.9 MeV and 87.4 MeV. Assuming the range-energy relation for protons to be at present better determined for Aluminium than for photographic emulsion, this experiment provides new information concerning the relation between particle range and energy in nuclear emulsion.RiassuntoSi è fatto un confronto fra i range di protoni artificialmente accelerati in alluminio e in emulsioni fotografiche Ilford G5. I range in emulsione furono ottenuti per misura diretta delle tracce delle particelle, quelli in alluminio con un metodo di attenuazione. I range dei protoni di tre differenti energie furono di 19.31, 13.23 e 7.82 g/cm2 in alluminio e di 22.85, 15.58 e 9.50 g/cm2 in emulsione di densità 3.791 g/cm3 condizionata a 58% di umidità relativa. Le corrispondenti energie erano 146.5 MeV, 117.9 MeV e 87.4 MeV. Assumendo che la relazione range-energia pei protoni sia attualmente meglio determinata per l’alluminio che per l’emulsione fotografica, il presente esperimento fornisce nuovi dati sulla relazione, nelle emulsioni nucleari, tra il range delle particelle e l’energia.

The interaction of fast K-mesons

SummaryTwo events are described in which heavy mesons interact with nuclei in photographic emulsions, producing small stars and emerging themselves from the collisions. In one example, a relativistic singly charged particle enters the stack and produces a star with only three emergent charged particles, which have been identified as a hyperon, a π-meson and a K-meson respectively. The K-meson creates two stars before it comes to rest and decays with the emission of a slow μ-meson. In the other example, a K-meson enters the stack from outside and, after interacting, comes to rest within the emulsion and decays with the emission of a single lightly ionizing particle. Certain features of interest associated with the scattering properties of heavy mesons are discussed.RiassuntoSi descrivono due eventi in cui mesoni pesanti interagiscono con nuclei dell’emulsione fotografica producendo piccole stelle ed emergendo essi stessi dalla collisione. In uno degli eventi una particella relativistica dotata di carica semplice entra nel pacco e produce una stella con sole tre particelle cariche emergenti che sono state identificate con un iperone, un mesone π e un mesone K, rispettivamente. Il mesone K produce due stelle prima di arrestarsi e decade con l’emissione di un mesone μ lento. Nell’altro evento un mesone K penetra nel pacco dall’esterno e, dopo aver interagito, si arresta nell’emulsione e decade con l’emissione di un’unica particella debolmente ionizzante. Si discutono alcuni interessanti particolarità riguardanti le proprietà dello scattering dei mesoni pesanti.

The production of heavy mesons and hyperons by π−-mesons of 4.5 GeV/c

SummaryA systematic investigation has been carried out, using nuclear photographic emulsions, into the production of heavy unstable particles by π−-mesons of 4.5 GeV/c. From 2854 stars, 4 hyperons and 4 heavy mesons were found which had velocities of less than 0.7c, and which satisfied certain geometrical selection criteria. One hyperon produces a secondary π-meson which comes to rest in the emulsion stack. The mass of this hyperon, shown to be negatively charged by the nuclear capture of its secondary particle, is (2352±5) mo.RiassuntoUsufruendo di emulsioni fotografiche nucleari si è eseguita una ricerca sistematica sulla produzione di particelle pesanti instabili dovuta a mesoni π− di 4.5 GeV/c. Nell’esame di 2548 stelle si sono trovati 4 iperoni e 4 mesoni pesanti con velocità inferiori a 0.7c e soddisfacenti a determinati criteri geometrici di selezione. Uno degli iperoni produce un mesone π secondario che si arresta nel pacco di emulsioni. La massa di questo iperone che, per la cattura della sua particella secondaria, risulta carico negativamente, è (2 352±5) me.