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Register a new userA new limit on the CP violating decay KS -> 3pi0 with the KLOE experiment
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We have carried out a new direct search for the CP violating decay KS -> 3pi0 with 1.7 fb^-1 of e+e- collisions collected by the KLOE detector at the phi-factory DAFNE. We have searched for this decay in a sample of about 5.9 x 10^8 KS KL events tagging the KS by means of the KL 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 KS 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 KS -> 2pi0 events in the same sample, we set the upper limit on BR(KS -> 3pi0 < 2.6 x 10^-8 at 90% C.L., five times lower than the previous limit. We also set the upper limit on the eta_000 parameter, |eta_000 | < 0.0088 at 90% C.L., improving by a factor two the latest direct measurement.
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The search for CP-violating K_Sto3pi^0 decay was performed with SND detector at VEPP-2M e^+e^- collider. The total amount of data corresponding to 7 million produced K_S mesons was analyzed. No candidate events were found, giving an upper limit of the decay branching ratio: Br(K_Sto3pi^0) < 1.4cdot10^{-5} at 90% confidence level.
We present a new result based on an analysis of the data collected by the MEG detector at the Paul Scherrer Institut in 2009 and 2010, in search of the lepton flavour violating decay mu->e gamma. The likelihood analysis of the combined data sample, which corresponds to a total of 1.8 x 10**14 muon decays, gives a 90% C.L. upper limit of 2.4 x 10**-12 on the branching ratio of the mu->e gamma decay, constituting the most stringent limit on the existence of this decay to date.
Based on an integrated luminosity of 1.61 fb$^{-1}$ $e^+e^-$ collision data collected with the KLOE detector at DA$Phi$NE, the Frascati $phi$-factory, a search for the $P$- and $CP$-violating decay $etatopi^{+}pi^{-}$ has been performed. Radiative $phitoetagamma$ decay is exploited to access the $eta$ mesons. No signal is observed in the $pi^{+}pi^{-}$ invariant mass spectrum, and the upper limit on the branching fraction at 90% confidence level is determined to be ${mathcal B}(etatopi^{+}pi^{-})<4.9times10^{-6}$, which is approximately three times smaller than the previous KLOE result. From the combination of these two measurements we get ${mathcal B}(etatopi^{+}pi^{-}) < 4.4times10^{-6}$ at 90% confidence level.
We have searched with the KLOE detector for the P and CP violating decay eta -> pi^+pi^- in a sample of 1.55 x 10^7 etas from the decay phi -> eta gamma of phi mesons produced in e+e- annihilations at DAFNE. No signal is found. We obtain the upper limit BR(eta -> pi^+pi^-) < 1.3 x 10^-5 at 90% confidence level.
We have searched for the decay KS->gg in a sample of 2x10^9 phi->KS KL decays collected at DAPHNE with an integrated luminosity of 1.9 fb^{-1}. KS are tagged by the KL interaction in the calorimeter. Two prompt photons must also be detected. Kinematic constraints reduce the initial 6x10^5 events to 2740 candidates, from which a signal of 711pm 35 events is extracted. By normalizing to the KS->2pi^0 decays counted in the same sample, we measure BR(KS->gg)= (2.26pm0.12_{stat}pm0.06_{syst})x10^{-6}, in agreement with O(p^4) Chiral Perturbation Theory predictions.
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