Summary
Systematic observations on 528 Λ0-θ0 production events in propane have yielded the following information: 1) There exists a neutral Λ0 decay; Λ0→π0 + n and the fraction of Λ0’s decaying in this mode is .32±.05. 2) The θ 01 component has a neutral decay mode, very probably θ 01 →θ0+π0. The θ0 therefore very probably has even spin. The fractionP(θ 01 → π0 + π0) /P(θ 01 → 2π) is .14±.06. The branching ratioP(Λ0 → π0 + n) /P(Λ0 → π− + n) is in good agreement with theI = 1/2 selection rule; the branching ratioP(θ0 → 2π0) /P(θ0 → π+ + π−) seems to be in disagreement. 3) (51±7.5)%, or just one half of the θ0 mesons escape the chamber and are to be identified with the θ 02 -meson proposed byGell-Mann andPais (4). The question of the existence of additional (parity doublet) decay modes is discussed. 4) The decays Λ0 → μ− + p + ν / e− + p + ν are not observed and the fraction of such decays is less than 2%. 5) The 3 particle decay modes of the θ 01 have not been observed and are therefore very unlikely to exceed 2% of all θ 01 decays. 6) Preliminary measurements yield lifetimesτ θ 01 =(.95 ± .08) · 10−10 s andτ Δ 0=(2.8 ± .2)·10−10 s. 7) For the θ 02 we obtain a lower limit of the lifetime, which together with the results ofLande et al. (5) brackets the θ 02 lifetime (3 < θ 02 < 10)·10−8 s.
Riassunto
L’osservazione sistematica di 528 eventi Λ0-θ0 in propano ha dato i seguenti risultati: 1) Esiste un decadimento Λ0 neutro; Λ0 → π0 + n e la frazione di Λ0 che decadono in questo modo è .32±.05. 2) La componente θ 01 ha un modo di decadimento neutro, molto probabilmente θ 01 → π0 + π0. Il θ0 ha pertanto molto probabilmente spin pari. La frazioneP(θ 01 → π0 + π0 /P(θ 01 → 2π) è .14±.06. Il rapportoP(Λ0 → π0 + n)/P (Λ0 → π− + n) è in buon accordo con la regola di selezioneI = 1/2; il rapportoP(θ0 → 2π0) /P(θ0 → π+ + π−) sembra invece in disaccordo. 3) (51 ± 7.5)%, cioè, metà dei mesoni θ0 sfuggono dalla camera e si debbono identificare con i mesoni θ 02 proposti daGell-Mann ePais (4). Si discute l’esistenza di altri modi di decadimento (doppietto di parità). 4) I decadimenti Λ0 → μ− + p + ν / e− + p + ν non si osservano e la frazione di tali decadimenti è inferiore al 2%. 5) I modi di decadimento del θ 01 in 3 particelle non sono stati osservati ed è pertanto assai poco probabile che eccedano il 2% del totale dei decadimenti di θ 01 . 6) Misure preliminari danno vite medieτ θ 01 = (.95 ± .08)·10−10 s eτ Δ 0 = (2.8±.2)·10−10s. 7) Per il θ 02 otteniamo per la vita media un limite inferiore che assieme ai risultati diLande et al. (5) inquadra la vita media di tale particella fra (3 < θ 02 < 10)·10−8s.
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Supported by a joint program of the Office of Naval Research and the Atomic Energy Commission.
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Eisler, F., Plano, R., Samios, N. et al. Systematics of Λ0 and θ0 decay. Nuovo Cim 5, 1700–1715 (1957). https://doi.org/10.1007/BF02856062
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DOI: https://doi.org/10.1007/BF02856062