Precise measurements of the ≠ meson and the neutral kaon masses with the KLOE detector

Abstract

We present precise measurements of the η and K 0 masses using the processes φηγ, ηγγ and φ → K S K L, K S→π +π -. The K 0 mass measurement, M K = 497.5830.005 stat0.020 syst MeV, is in acceptable agreement with the previous measurements but is more accurate. We find m η = 547.8740.007 stat0.029 syst MeV. Our value is the most accurate to date and is in agreement with two recent measurements based on η decays, but is inconsistent, by about 10σ, with a measurement of comparable precision based on η production at threshold. © SISSA 2007.