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

The lifetimes of both positive and negative relativistic ( gamma =29.33) muons have been measured in the CERN Muon Storage Ring with the results tau /sup +/=64.419 (58) mu s, tau /sup -/=64.368 (29) mu s. 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 /sup -3/ at 95% confidence. Assuming special relativity, the mean proper lifetime for mu /sup -/ is found to be tau /sub 0//sup - /=2.1948 (10) mu s the most accurate value reported to date. The agreement of this value with previously measured values of tau /sub 0 //sup +/ confirms CPT invariance for the weak interaction in muon decay. (39 refs).