TInvariance and the Unitarity Limit inKL0→μ+μ−

Abstract

The role of $T$ invariance in the unitarity (lower) limit of the decay $K_L^0\to {\mu }^{+}{\mu }^{-}$ is examined. We note that the assumption of $T$ invariance is necessary only insofar as $\epsilon$, the $\mathrm{CP}$-violating parameter in the neutral $K$ system, is nonzero. Because of the smallness of this parameter, a chance cancellation appears unlikely. Therefore, the unitarity (lower) limit for $K_L^0\to {\mu }^{+}{\mu }^{-}$ can be decreased only (with the above exception) by including in the unitarity sum intermediate states other than the two-photon state (e.g., three-pion states).