Measurement of the KL meson lifetime with the KLOE detector
  We present a measurement of the KL lifetime using the KLOE detector. From a sample of 4 x 10^8 KS KL pairs following the reaction e+ e- -> phi -> KS KL we select 15 x 10^6 KL -> p0 p0 p0 decays tagged by KS -> pi+ pi- events. From a fit of the proper time distribution we find tau_L = (50.92 +- 0.17{stat} +- 0.25{syst})$ ns. This is the most precise measurement of the KL lifetime performed to date. 
The KLOE collaboration