Search for the $K_S to 3 π^0$ decay with the KLOE detector

The $K_S \to 3 π^0$ decay is a pure CP violating process which, assuming CPT invariance, allows one to investigate direct CP violation. This decay has not been observed so far, and the best upper limit on the branching ratio $BR(K_S to 3π^0) < 1.2 \cdot 10^{-7}$ is two orders of magnitude larger than predictions based on the Standard Model: $BR(K_S \to 3π^0) \sim 2 \cdot 10^{-9}$. In this article we present the search for the $K_S \to 3π^0$ decay performed with the KLOE detector operating at the DAFNE Φ-factory at the Frascati Laboratory. We describe the analysis techniques used in the background rejection and signal events selection as well as the evaluation of almost five times lower upper limit on the $K_S \to 3π^0$ branching ratio. We discuss shortly also the perspectives for a new measurement using the KLOE-2 apparatus equipped with a new inner tracker and the calorimeters at low theta angle.

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