Effect of the Hyperfine Splitting of aμ-Mesonic Atom on Its Lifetime

The lifetime of a $\mu$-mesonic atom depends on its hyperfine state because of the spin dependence of the interaction between the ${\mu }^{-}$ meson and the capturing proton. The small lifetime difference between the hyperfine states is estimated in a one-particle model. Possible experimental detection of such a difference is discussed.