Eta decays studies with KLOE.

We present the status of the analyses on η meson decays with the KLOE detector at DAΦNE Φ factory[1]. The KLOE detector has collected about 20 milions of η events, produced by the Φ → ηγ decay process. Here we present the status of the analyses of the decay process: η → 3γ, η → π+π−π0, η → 3π0, η → π0γγ and η → π+π−γ. The η → 3γ decay is a C violating decay. The SM prediction of the branching ratio is of the order of 10−12[2], far below the present experimental limit (5×10−4 [3]), so any measurement of a larger branching ratio would be a clear signal of new physics. KLOE has analyzed 17×106 η decays [4]. No signal has been found, so we have evaluated an upper limit: Br(η → 3γ) < 1.6 × 10−5 (95 % C.L.). The η → π0γγ is interesting for testing ChPT to O(p6) level [2]. We expect to have from 5000 to 14000 such decays in our data[3][2]. The main background is the η → 3π0 channel when there is a merging of the clusters in the calorimeter. The Dalitz plot analysis of the η → π+π−π0 channel is interesting for C vio- lation and for ChPT testing [2]. We have analized about 400000 η → 3π0 events, producing the following very preliminary results for the Dalitz plot parameters: (a,b,c) = (−1.05 ± 0.01, 0.20 ± 0.03, −0.009 ± 0.009) (only statistical error re- ported). The c parameter is compatible with 0, so no C violation is observed. For the η → 3π0 the overall selection efficiency is 16%. So we expect to have a sample of 1 million events with the full KLOE statistic. The analysis reproduces well the Dalitz plot parameter put in the MC generator. The η → π+π−γ is an interesting decay to check the box anomaly [2] studying the energy distribution of the γ. We have selected 18508 among 1 million of η events with a preliminary analysis.