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

• DOI: 10.1007/bf02738571
• Publication Date: 2007-12-18T09:19:59Z
• Authors: A. Bertin; G. Carboni; A. Placci; E. Zavattini; U. Gastaldi; G. Gorini; G. Neri; O. Pitzurra; E. Polacco; G. Torelli; A. Vitale; J. Duclos; J. Picard
• Keywords: Metastability

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 fractione 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 ofe 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.