A new limit on the CP violating decay $K_{S}\rightarrow 3\pi ^{0}$ with the KLOE experiment

We have carried out a new direct search for the CP violating decay $K_{S}\rightarrow 3\pi ^{0}$ with $1.7 fb^{-1}$ of $e^{+}e^{-}$ collisions collected by the KLOE detector at the $\phi$ -factory DA$\Phi$ NE. We have searched for this decay in a sample of about $5.9 \times 10^{8} K_{S}K_{L}$ events tagging the $K_{S}$ by means of the $K_{L}$ interaction in the calorimeter and requiring six prompt photons. With respect to our previous search, the analysis has been improved by increasing of a factor four the tagged sample and by a more effective background rejection of fake $K_{S}$ tags and spurious clusters. We find no candidates in data and simulated background samples, while we expect 0.12 standard model events. Normalizing to the number of $K_{S}\rightarrow 2\pi ^{0}$ events in the same sample, we set the upper limit on $BR\left ( K_{S}\rightarrow 3\pi^{0} \right )\leqslant 2.6 \times 10^{-8}$ at 90% C.L., five times lower than the previous limit. We also set the upper limit on the $\eta _{000}$ parameter, $\mid \eta _{000}\mid\leqslant 0.0088$ at 90% C.L., improving by a factor two the latest direct measurement