CPT Tests: Kaon vs Neutrinos

CPT violation has an impressive limit in the neutral kaon system |m(K^0) - m(\bar{K}^0)| < 10^{-18} m_K = 0.50 \times 10^{-18} GeV. However, if viewed as a constraint on the mass-squared, the bound appears weak, |m^2(K^0) - m^2(\bar{K}^0)| < 0.25 eV^2. We point out that neutrino oscillation offers better limits on CPT violation in this case. The comparison of solar and rector neutrino results puts the best limit on CPT violation by far, |\Delta m^2_\nu - \Delta m^2_{\bar{\nu}}| < 1.3 \times 10^{-3} eV^2 (90% CL).