Molecular-ion formation byαμ−andαπ−atoms in liquid helium

Abstract

The experimentally determined intensities of x rays due to muonic and pionic atoms formed in gaseous and liquid helium are analyzed. The analysis is based largely, though not entirely, on some estimates of Auger rates. A discussion of Stark transitions, some estimates of the time required to slow a recoiling mesonic atom after it ejects an electron from a nearby atom in liquid helium, and a brief discussion of kaonic x-ray intensities are also employed. It is concluded that an $\ensuremath{\alpha}{\ensuremath{\mu}}^{\ensuremath{-}}$ or an $\ensuremath{\alpha}{\ensuremath{\pi}}^{\ensuremath{-}}$ atom in liquid helium probably becomes temporarily bound to a helium atom during its cascade to the $1s$ state. More specifically, it is argued that the relatively intense muonic $K\ensuremath{\gamma}$ line in gas, the relatively faint muonic and pionic $K\ensuremath{\gamma}$ lines in liquid, and the anomalously high $\frac{K\ensuremath{\beta}}{K\ensuremath{\alpha}}$ intensity ratio for pions in liquid indicate that molecular ions are probably formed in liquid but not in gas by $\ensuremath{\alpha}{\ensuremath{\mu}}^{\ensuremath{-}}$ and $\ensuremath{\alpha}{\ensuremath{\pi}}^{\ensuremath{-}}$ atoms with $n=4$.