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Register a new userSearch for the K(S) --> e+e- decay with the KLOE detector at DAFNE
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The KLOE collaboration
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We present results of a direct search for the decay KS --> e+e- with the KLOE detector, obtained with a sample of e+e- --> phi --> KSKL events produced at DAFNE, the Frascati phi-factory, for an integrated luminosity of 1.3fb-1. The Standard Model prediction for this decay is BR(KS --> e+e-) = 1.6*10^-15. The search has been performed tagging the KS decays by simultaneous detection of a KL interaction in the calorimeter. Background rejection has been optimized by using both kinematic cuts and particle identification. At the end of the analysis chain we find BR(KS --> e+e-) < 2.1*10^-8 at 90% CL, which improves by a factor of ~7 on the previous best result, obtained by CPLEAR experiment.
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We present the result of a direct search for the decay K_S -> e+e-, obtained with a sample of e+e- -> phi -> K_S K_L events produced at DAFNE, the Frascati phi-factory, for an integrated luminosity of 1.9 fb^-1. The search has been performed using a pure K_S beam tagged by the simultaneous detection of a K_L interaction in the calorimeter. Background rejection has been optimized by using both kinematic and particle identification cuts. We find BR(K_S -> e+e-) < 9x10^-9 at 90% CL, which improves by an order of magnitude on the previous best limit.
We have studied the vector to pseudoscalar conversion decay phi -> eta e+e-, with eta -> pi0pi0pi0, with the KLOE detector at DAPHNE. The data set of 1.7 fb-1 of e+e- collisions at sqrt(s)~Mphi contains a clear conversion decay signal of ~31,000 events from which we measured a value of BR(phi -> eta e+e-)=(1.075+-0.007+-0.038)x10-4. The same sample is used to determine the transition form factor by a fit to the e+e- invariant mass spectrum, obtaining b(phi eta) =(1.17 +- 0.10 + 0.07) GeV-2, that improves by a factor of five the precision of the previous measurement and is in good agreement with VMD expectations.
A search for the process $e^+e^- to eta^prime$ has been performed with the SND detector at the VEPP-2000 $e^+e^-$ collider. The data were accumulated at the center-of-mass energy of $957.78pm 0.06$ MeV with an integrated luminosity of about 2.9 pb$^{-1}$. For reconstruction of the $eta^prime$ meson five decay chains have been used: $eta^{prime}toetapi^+pi^-$ followed by the $eta$ decays to $gammagamma$ and $3pi^0 $, and $eta^{prime} to etapi^0pi^0$ followed by the $eta$ decays to $pi^+pi^-pi^0$, $gammagamma$, and $3pi^0$. As a result, the upper limit has been set on the $eta^prime$ electronic width: $Gamma_{eta^{prime}to e^+e^-} < 0.0020$ eV at the 90% confidence level.
We report the first observation of the rare eta->e+e-e+e- decay based on 1.7 fb^{-1} collected by the KLOE experiment at the DAFNE phi-factory. The selection of the e+e-e+e- final state is fully inclusive of radiation. We have identified 362 +- 29 events resulting in a branching ratio of (2.4 +- 0.2_stat+bckg +- 0.1_syst) x 10^{-5}.
Using ~600 pb-1 collected with the KLOE detector at DAPhiNE, we have studied the production cross section of pi+ pi- pi0 pi0 and p0p0 gamma final states in e+e- collisions at center of mass energies between 1000 and 1030 MeV. By fitting the observed interference pattern around Mphi for both final states, we extract a measurement (preliminary) for the ratio Gamma(omega -> pi0 gamma)/Gamma(omega -> pi+ pi- pi0) = 0.0934 +- 0.0022. Since these two final states represent the 98% of the omega decay channels, we use unitarity to derive BR(omega -> pi+pi-pi0)= (89.94 +- 0.23)% and BR(omega -> pi0 gamma) = (8.40 +- 0.19)%. Moreover, the parameters describing the e+e- -> pi+ pi- pi0 pi0 reaction around Mphi are used to extract the branching fraction for the OZI and G-parity violating phi -> omega pi0 decay: BR(phi -> omega pi0) = (5.63 +- 0.70) x 10^-5.
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