Lifetime of the2SState ofHe+

Abstract

The lifetime of the $2S$ state of ${\mathrm{He}}^{+}$ has been measured by counting decay photons versus time from an ensemble of excited ${\mathrm{He}}^{+}$ ions stored in an electromagnetic trap of the Penning type. The result is ${\tau }_{2S}=1.922\mathrm{}\left(82\right)\mathrm{}$ msec. This is in agreement with the theoretical value of 1.899 msec. The agreement between theory and experiment implies a new upper limit on the amount of parity impurity in the $2S$ wave function.