Measurements of relativistic time dilatation for positive and negative muons in a circular orbit

The lifetimes of both positive and negative relativistic (γ = 29.33) muons have been measured in the CERN Muon Storage Ring with the results τ⁺ = 64.419 (58) µs, τ^- = 64.368 (29) µs The value for positive muons is in accordance with special relativity and the measured lifetime at rest: the Einstein time dilation factor agrees with experiment with a fractional error of 2×10^-3 at 95% confidence. Assuming special relativity, the mean proper lifetime for μ^- is found to be τ₀^- = 2.1948(10) µs the most accurate value reported to date. The agreement of this value with previously measured values of τ₀⁺ confirms CPT invariance for the weak interaction in muon decay.