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Experimental study on the (μ 4He) +2S metastable system in helium gas

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Il Nuovo Cimento B (1971-1996)

Summary

We report the results of an experimental investigation on the properties of the (μ 4He) +2S metastable muonic system, which was performed stopping negative muons in a pure helium target at pressures ranging from 10 to 50 atm, and observing the total yield and the differential time distribution of the X-rays released in delayed coincidence with the arrival of muons. At each pressureP, information was obtained on the following quantities:a) the total disappearance rate λ2S,tot(P) of the (μ 4He) +2S system,b) the disappearance rates λA(P) and λSt(itP) of the (μ 4He) +2S system for external Auger effect and Stark-mixing collisions,c) the fractionε 2S of muons stopped in helium which form the (μ 4He) +2S system. The results obtained on λ2S,tot(P) are in agreement with the results of a cascade calculation, which was performed requiring consistency with previous experimental results; the present measurements show that the variation ofε 2S (P) with pressure in the range (7÷50) atm is small. Good agreement was found between the values for the two-quantum decay rate λ2X of the (μ 4He) +2S system derived from the present data and the theoretical predictions. The results obtained on λ2S,tot(P), instead, are somewhat in conflict with the results of a recent calculation on λ2St(P). The possible reasons of such disagreement are discussed, referring to possible clustering effects of the helium atoms around the (μHe+ ion.

Riassunto

Presentiamo i risultati di un esperimento sulle proprietà del sistema muonico metastabile (μHe) +2S . L'esperimento è stato condotto fermando muoni negativi in un bersaglio di elio puro a pressioni comprese fra 10 e 50 atmosfere, ed osservando il numero totale e la distribuzione temporale dei raggi X emessi in coincidenza ritardata rispetto all'arrivo dei muoni. Ad ogni pressioneP, si sono ottenute informazioni sulle seguenti quantità:a) la velocità totale di decadimento λ2S,tot(P) del sistema (μHe) Emphasis>+2S ;b) le velocità di decadimento λA(P) e λ St (P) del sistema (μHe) +2S per effetto Auger esterno e per urti che provochino mescolamento Stark,c) la frazione ε2S(P) di muoni fermati in elio che formano il sistema (μHe) +2S . I risultati ottenuti suε 2S(P) sono in accordo con i risultati di un calcolo sul processo di cascata elettromagnetica, che è stato ottenuto richiedendo consistenza con risultati sperimentali precedenti. Le presenti misure mostrano che la variazione diε 2S(P) con la pressione nell'intervallo (7÷50) atm è piccola. Si è trovato un buon accordo fra i valori della velocità λ2X di decadimento del sistema (μHe) +2S mediante emissione di due fotoni derivati dai dati presenti e le previsioni teoriche. I risultati ottenuti per λ2S,tot(P), invece, sono in disaccordo con i risultati di una recente stima di λ2St (P). Le possibili regioni di tale disaccordo sono discusse, riferendole a possibili effetti diclustering degli atomi di elio attorno allo ione (μHe) +2S .

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Author notes

  1. A. Bertin

    Present address: Istituto di Fisica dell'Università, Pisa

  2. G. Carboni

    Present address: Sezione di Pisa, Istituto Nazionale di Fisica Nucleare, Pisa

  3. G. Neri

    Present address: ENEL, Larderello

  4. O. Pitzurra

    Present address: ETH, Zurich

Authors and Affiliations

  1. CERN, Geneva

    A. Bertin, G. Carboni, A. Placci & E. Zavattini

  2. Istituto di Fisica dell'Università, Pisa

    U. Gastaldi, G. Gorini, G. Neri, O. Pitzurra, E. Polacco & G. Torelli

  3. Sezione di Pisa, Istituto Nazionale di Fisica Nucleare, Pisa

    U. Gastaldi, G. Gorini, G. Neri, O. Pitzurra, E. Polacco & G. Torelli

  4. Sezione di Bologna, Istituto Nazionale di Fisica Nucleare, Bologna

    A. Vitale

  5. Centre d'Etudes Nucléaires de Saclay, Gif-sur-Yvette

    A. Vitale, J. Duclos & J. Picard

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  1. A. Bertin
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Bertin, A., Carboni, G., Placci, A. et al. Experimental study on the (μ 4He) +2S metastable system in helium gas. Nuov Cim B 26, 433–480 (1975). https://doi.org/10.1007/BF02738571

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