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Register a new userUpper Limit on the eta to gamma gamma gamma Branching Ratio with the KLOE Detector
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We have searched for the C-violating decay eta to gamma gamma gamma in a sample of ~ 18 million eta mesons produced in phi to eta gamma decays, collected with the KLOE detector at the Frascati phi-factory DAFNE. No signal is observed and we obtain the upper limit BR(eta to gamma gamma gamma) less equal than 1.6x10^(-5) at 90 % C.L.
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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 present a measurement of {eta} meson production in photon-photon interactions produced by electron-positron beams colliding with sqrt{s}=1 GeV. The measurement is done with the KLOE detector at the phi-factory DA{Phi}NE with an integrated luminosity of 0.24 fb^{-1}. The e^+e^- --> e^+e^-{eta} cross section is measured without detecting the outgoing electron and positron, selecting the decays {eta}-->{pi}^+{pi}^-{pi}^0 and {eta}-->{pi}^0{pi}^0{pi}^0. The most relevant background is due to e^+e^- --> {eta}{gamma} when the monochromatic photon escapes detection. The cross section for this process is measured as {sigma}(e^+e^- -->{eta}{gamma}) = (856 pm 8_{stat} pm 16_{syst}) pb. The combined result for the e^+e^- -->e^+e^-{eta} cross section is {sigma}(e^+e^- -->e^+e^-{eta}) = (32.72 pm 1.27_{stat} pm 0.70_{syst}) pb. From this we derive the partial width {Gamma}({eta}-->{gamma}{gamma}) = (520 pm 20_{stat} pm 13_{syst}) eV. This is in agreement with the world average and is the most precise measurement to date.
The ratio R_{eta}=Gamma(eta -> pi^+pi^-gamma)/Gamma(eta -> pi^+pi^-pi^0) has been measured by analyzing 22 million phi to eta gamma decays collected by the KLOE experiment at DAPhiNE, corresponding to an integrated luminosity of 558 pb^{-1}. The eta to pi^+pi^-gamma proceeds both via the rho resonant contribution, and possibly a non-resonant direct term, connected to the box anomaly. Our result, R_{eta}= 0.1856pm 0.0005_{stat} pm 0.0028_{syst}, points out a sizable contribution of the direct term to the total width. The di-pion invariant mass for the eta -> pi^+pi^-gamma decay could be described in a model-independent approach in terms of a single free parameter, alpha. The determined value of the parameter alpha is alpha = (1.32 pm 0.08_{stat} +0.10/-0.09_{syst}pm 0.02_{theo}) GeV^{-2}
We have analyzed 1.62 fb$^{-1}$ of $e^{+}e^{-}$ collisions at a center of mass energy $sim M_{phi}$ collected by the KLOE experiment at DA$Phi$NE. This sample corresponds to a production of $sim$ 1.7 billion of $ks$ $kl$ pairs which allowed us to search for the rare $K_Sto gammagamma$ decay. $K_S$ are tagged by the $K_L$ interaction in the calorimeter and the signal is searched for by requiring two additional prompt photons. Strong kinematic requirements reduce the initial 0.5$times 10^6$ events to 2300 candidates from which we extract a signal of 600 $pm$ 35 events. By normalizing to the $ks to 2 pi^0$ decays counted in the same sample, the measured value of BR($ks to gammagamma$) is (2.27 $pm 0.13(stat.) ^{+0.03}_{-0.04} (syst.)) times 10^{-6}$, in agreement with $O(P^4)$ Chiral Perturbation Theory predictions.
We have measured the absolute branching ratio of the K+ -> pi+ pi0 (gamma) decay, using about 20 million tagged K+ mesons collected with the KLOE detector at DAFNE, the Frascati phi-factory. Signal counts are obtained from the fit of the distribution of the momentum of the charged decay particle in the kaon rest frame. The result, inclusive of final-state radiation, is BR(K+ -> pi+ pi0 (gamma))=0.2065+/-0.0005_{stat}+/- 0.0008_{syst}.
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