Measurement of the Auger effect in the ($\mu^{4}$He$)$\^{+}\_{2s}$

The authors present some results of an experimental study which was performed to evaluate the contribution of the external Auger effect on the de-excitation of the ( mu /sup 4/He)/sub 2s//sup +/ system. Such a metastable system is formed when negative muons are slowed down in a helium target; the muons, initially captured in highly excited levels, promptly (in a time of 10/sup -11/s and through an electromagnetic cascade) reach either the fundamental level 1s or, with a small probability, the 2s level. In addition to the Auger effect, the muonic atom, once formed, can also disappear through other channels. (3 refs) .