First results from phi ->KL KS decays with the KLOE detector

The KLOE experiment has collected 2.4 pb − 1 of integrated luminosity during the commissioning of the DAΦNE φ -factory in 1999. The performance of the detector has been studied using the φ → K L K S decays collected during this period, yielding also first measurements of relevant K parameters such as masses and lifetimes. A clean K S → π + π − sample is used to select K L → π + π − CP-violating decays and K L → K S regeneration events in the detector material. Results on the regeneration probability in a beryllium-alluminum alloy and carbon-fiber plus aluminum composite are presented.