In this paper the details of a previously reported precise measurement of the $\frac{K^{+}}{K^{-}}$ lifetime ratio are described. Using a separated beam at the Brookhaven AGS, we have counted the fraction of 1.6- and 2.0-GeV/c $K$ mesons surviving at distances up to 2000 in. The result of the measurement yields $\frac{\tau \left(K^{+}\right)}{\tau \left(K^{-}\right)}-1=-0.00090\mathrm{}\pm 0.00078$, indicating no violation of the $\mathrm{CPT}$ theorem. No evidence for deviations from an exponential decay law or for the existence of long-lived $K$ mesons was found. The upper limit for any long-lived $K$ mesons in the beam is 3×${10}^{-3\mathrm{}}$ at the 90% confidence level.

• Received 10 April 1969

DOI:https://doi.org/10.1103/PhysRev.185.1676