Abstract
We present a new search for the KS → 3π0 decay performed with the KLOE detector operating at the DAΦNE ϕ-factory. The KS mesons were tagged via registration of KL mesons which crossed the drift chamber without decaying and interacted with the KLOE electromagnetic calorimeter. The KS → 3π0 decay was then searched requiring six prompt photons. To suppress background, originating from fake KS tags and KS → 2π0 decays with additional two spurious clusters, we have performed a discriminant analysis based on kinematical fit, testing of the signal and background hypotheses and exploiting of the differences in kinematics of the KS decays into 2π0 and 3π0. In a sample of about 1.7·109 ϕ → KSKL events we have found no candidates in data and simulated background samples. Normalizing to the number of KS → 2π0 events in the same sample, we have set the upper limit on the KS → 3π0 branching ratio BR(KS → 3π0) < 2.6 · 10−8 at 90% C.L., five times lower than the previous limit. This upper limit can be translated into a limit on the modulus of the η000 parameter amounting to |η000| < 0.0088 at 90% C.L., improving by a factor two the latest direct measurement.
Highlights
Since the first discovery of the CP–violating neutral kaon decay in 1964, there has been made a big effort to describe the CP symmetry breaking within the Standard Model
In this article we briefly describe the search of the KS → 3π0 decay based on the 1.7 fb−1 of integrated luminosity gathered with the KLOE detector operating at the φ–factory DAΦNE of the Frascati Laboratory [5]
We have estimated an upper limit on the KS → 3π0 branching ratio taking into account systematic uncertainties related to the number of background events and to the determination of the acceptance and selection efficiencies for the signal and normalization samples
Summary
Since the first discovery of the CP–violating neutral kaon decay in 1964, there has been made a big effort to describe the CP symmetry breaking within the Standard Model. At present the main experimental effort is focused on the neutral B and D meson system studies. There are still several interesting open issuses in the kaon physics, which can contribute to our better understanding of the CP violation mechanism [1]. KS decays to |π+π−π0 and |3π0 , requiring CP violation, are still poorly known. The |π+π−π0 final state can be produced in neutral kaon decays with isospin I = 0, 1, 2, or 3. The I = 0 and I = 2 states have CP = 1, and KS can decay into them without violation of the CP symmetry.
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