η, η' Studies with the KLOE Detector at DAΦNE

The KLOE detector is operational since spring '99 at DA?NE, the Frascati e+e- collider, a -factory running at 1.02 GeV c.m. energy. This detector has been designed and built with the primary goal of measuring Re(?' / ?), the CP violation parameter in the kaon system, with a sensitivity of about one part in ten thousands. Apart from CP studies in the kaon system, KLOE has a rich scientific program that can be exploited with an integrated luminosity not far from the one which has already been collected, namely the study of decays into scalar and pseudoscalar mesons, the measurement of the hadronic cross-section up to 1 GeV, rare kaon decays, decays into three pions. Since the detector installation there have been three periods of stable data taking and a total amount of ~200 pb-1 has been collected by end of 2001, corresponding to ~6.7 ? 108 mesons and to ~8.7 ? 106 ? mesons, being BR( ? ??) = (1.297?0.033) ? 10-2. We present the results obtained, for a data sample of 17 pb-1 collected in the year 2000, for ? ?? and ? ?'?: the ratio of these two BR's has been measured to be (5.3 ? 0.5 ? 0.4) ? 10-3, leading to a very accurate determination of the mixing angle in the flavor basis P = (40+7.5-1.5)? and to the most accurate determination of BR( ? ?'?) to date; (6.8 ? 0.6 ? 0.5) ? 10-5. From the ratio BR( ? ?'?)/BR( ? ?0?) we have extracted the value BR( ? ?0?) = (1.377 ? 0.007 ? 0.05) ? 10-3.