Measurement of the KL meson lifetime with the KLOE detector

Abstract We present a measurement of the K L lifetime using the KLOE detector. From a sample of ∼ 4 × 10 8 K S K L pairs following the reaction e + e − → ϕ → K S K L we select ∼ 15 × 10 6 K L → π 0 π 0 π 0 decays tagged by K S → π + π − events. From a fit of the proper time distribution we find τ L = ( 50.92 ± 0.17 stat ± 0.25 syst ) ns . This is the most precise measurement of the K L lifetime performed to date.