Precision Lifetime Measurements on Positive and Negative Muons

An experiment to measure and compare the free decay rates of positive and negative muons is described. Muons from the Nevis synchrocyclotron were stopped in a liquid-hydrogen target containing less than 1 ppm ${\mathrm{D}}_2$ and less than 1 part in ${10}^9$ of other impurities. In this situation, the rate of ${\mu }^{-}$ capture in ${\mathrm{H}}_2$ was the only significant correction to the free decay rate of ${\mu }^{-}$ and was measured in a separate experiment. The lifetimes were monitored by measuring the time intervals between muon stops and decay electrons using a transistorized digitron of 30-nsec channel width. Electronic circuitry of the "interference remover" type was employed to eliminate time-dependent background. ${\mu }^{-}$ and ${\mu }^{+}$ lifetimes were measured with the same apparatus and under essentially the same conditions of rate and geometry. The ratio of the lifetimes is expected to be particularly insensitive to any systematic errors. We have obtained: ${\tau }_{{\mu }^{-}}=2.198\mathrm{}\pm 0.002$ μsec (hydrogen correction made), ${\tau }_{{\mu }^{+}}=2.197\mathrm{}\pm 0.002$ μsec, $R=\frac{{\tau }_{{\mu }^{-}}}{{\tau }_{{\mu }^{+}}}=1.000\mathrm{}\pm 0.001$.