Di Micco, B (reprint author), Univ Rome Tre, Dipartimento Fis, Rome, Italy.
We present precise measurements of the eta and K-0 masses using the processes phi -> eta gamma, eta -> gamma gamma and phi -> KSKL, K-S -> pi(+)pi(-). The K-0 mass measurement, M-K = 497.583 +/- 0.005(stat) +/- 0.020(syst) MeV, is in acceptable agreement with the previous measurements but is more accurate. We find m(eta) = 547.874 +/- 0.007(stat) +/- 0.029(syst) MeV. Our value is the most accurate to date and is in agreement with two recent measurements based on eta decays, but is inconsistent, by about 10 sigma, with a measurement of comparable precision based on eta production at threshold.