PRECISE MEASUREMENT OF THE LAMBDA-0 AND LAMBDA-OVER-BAR(0) MASSES AND A TEST OF CPT INVARIANCE

A precision measurement of the masses of the Λ0 and Λ¯0 hyperons is obtained from Gaussian fits to the invariant mass distributions for 20 138 Λ0’s and 18 309 Λ¯0’s. The Gaussians have standard deviations of 0.49 and 0.51 MeV/c2 for the Λ0 and Λ¯0, respectively. Systematic errors were reduced by calibrating the spectrometer with 60 000 exclusive events containing a KS0. We find MΛ=1115.678±0.006±0.006 MeV/c2 and MΛ¯=1115.690±0.008±0.006 MeV/c2. The Λ0−Λ¯0 mass difference testing CPT invariance is -0.012±0.010 MeV/c2.