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Register a new userMeasurement of the branching ratio and search for a CP violating asymmetry in the eta -> pi+pi-e+e-(gamma) decay at KLOE
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We have studied the eta->pi+pi-e+e-(gamma) decay using about 1.7 fb^-1 collected by the KLOE experiment at the DAFNE phi-factory. This corresponds to about 72 millions eta mesons produced in phi radiative decays. We have measured the branching ratio, inclusive of radiative effects, with 4% accuracy: BR(eta->pi+pi-e+e-(gamma)) = (26.8 +/- 0.9_Stat. +/- 0.7_Syst.) x 10^-5. We have obtained the first measurement of the CP-odd pipi-ee decay planes angular asymmetry, A_phi = (-0.6 +/- 2.5_Stat. +/- 1.8_Syst.) x 10^-2.
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The reaction pd->3He eta at threshold was used to provide a clean source of eta mesons for decay studies with the WASA detector at CELSIUS. The branching ratio of the decay eta->pi+pi-e+e- is measured to be (4.3+/-1.3+/-0.4)x10^-4.
The rare decay $eta to pi^+ pi^- e^+ e^-$ is studied using a sample of $1.3 times 10^9$ $J/psi$ events collected with the BESIII detector at BEPCII in 2009 and 2012. The branching fraction is measured with improved precision to be $left( 2.42pm0.05_{stat.}pm0.08_{syst.} right) times 10^{-3}$. Due to the inclusion of new data, this result supersedes the last BESIII result on this branching fraction. In addition, the CP-violating asymmetry in the angle between the decay planes of the $pi^+pi^-$-pair and the $e^+e^-$-pair is investigated. A measurable value would indicate physics beyond the standard model; the result is $mathcal{A}_{CP} = left(2.9pm3.7_{stat.}pm1.1_{syst.} right)%$, which is consistent with the standard model expectation of no CP-violation. The precision is comparable to the asymmetry measurement in the $K^0_Ltopi^+pi^-e^+e^-$ decay where the observed $(14pm2)%$ effect is driven by a standard model mechanism.
We present the current status of the analysis of about 1.7 billion KSKL pair events collected at DAFNE with the KLOE detector to determine the branching ratio of KS -> pi e nu decay and the lepton charge asymmetry. This sample is ~4 times larger in statistics than the one used in a previous KLOE analysis, allowing us to improve the accuracy of the measurement and of the related tests of CPT symmetry and Delta S = Delta Q rule.
The PEN Collaboration is conducting a new measurement of the pi+ -> e+ nu branching ratio at the Paul Scherrer Institute, with the goal uncertainty of delta B/B(pie2)=5E-4 or lower. At present, the combined accuracy of all published pie2 decay measurements lags behind the theoretical calculation by a factor of 40. In this contribution we report on the PEN detector configuration and its performance during two development runs done in 2007 and 2008.
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}
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