Summary
An experiment is reported on the parity-violating reaction d(α, γ)6Li, leading to theJ P=0+,I=1,E x =3.562 MeV state, which, being a ΔI=1 transition, could be strongly enhanced by the presence of neutral currents in hadronic weak interactions in nuclei. The experiment has been carried out by exposing a deuterium target to a beam of α-particles reaching the resonant energy in the region in the middle of the tube containing the gas. Gamma-rays from this region are detected by a 90 cm3 Ge(Li) counter connected to a 4096 channel analyser through an amplifying and analysing chain. The various sources of the background of spurious counting in the Ge(Li) and the procedure adopted to reduce their effect are discussed. We find no evidence for a nonzero parity-violating width of the 3.562 MeV state of6Li and can set an upper limit for this width of 8·10−4 eV, which is an order of magnitude or more lower than that obtained in the previous experiments on this reaction.
Riassunto
Si riferiscono i risultati di un’esperienza sulla reazione violante la parità d(α, γ)6Li che porta al livelloJ P=0+,I=1,E x =3.562 MeV, che varia di uno l’isospin. Essa dovrebbe quindi essere fortemente intensificata dalla presenza delle correnti neutre nelle interazioni deboli nei nuclei. Si è compiuto l’esperimento esponendo un bersaglio di deuterio ad un fascio di particelle α, che raggiungevano l’energia di risonanza in una zona a metà del tubo che conteneva il gas. I raggi gamma provenienti da questa zona venivano rivelati da un contatore Ge(Li) di 90 cm3 di volume collegato a mezzo di una catena di amplificazione e stabilizzazione ad un analizzatore a 4096 canali. Si discutono le varie fonti del fondo di conteggi spuri del Ge(Li) ed i procedimenti adottati per ridurre l’effetto. Non si trovano prove per valori diversi da zero della larghezza violante la parità del livello a 3.562 MeV e si stabilisce un limite superiore di 8·10−4 eV per questa larghezza. Tale limite è inferiore di uno o più ordini di grandezza a quelli ottenuti nelle esperienze precedenti su questa reazione.
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This experiment was made possible by the continuous and intelligent help by Mr. F. PANZERI.
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Bellotti, E., Fiorini, E., Negri, P. et al. An experiment on isospin-changing parity violation involving hadrons in nuclei. Nuov Cim A 29, 106–122 (1975). https://doi.org/10.1007/BF02735415
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DOI: https://doi.org/10.1007/BF02735415