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Register a new userUpper Limit on the Decay K+ --> e+ nu mu+ mu-
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An upper limit on the branching ratio for the decay K+ --> e+ nu mu+ mu- is set at 5.0 x 10^{-7} at 90% confidence level, consistent with predictions from chiral perturbation theory.
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Experiment 865 at the Brookhaven AGS obtained 410 K+ -> e+ nu e+e- and 2679 K+ -> mu+ nu e+e- events including 10% and 19% background. The branching ratios were measured to be (2.48+-0.14(stat.)+-0.14(syst.))x10^-8 (m_ee>150 MeV) and (7.06+-0.16+-0.26)x10^-8 (m_ee>145 MeV), respectively. Results for the decay form factors are presented.
The decay K- -> pi0 mu- nu has been studied using in-flight decays detected with the ISTRA+ spectrometer. About 540K events were collected for the analysis. The lambda+ and lambda0 slope parameters of the decay form-factors f+(t), f0(t) have been measured : lambda+ = 0.0277+-0.0013 (stat)+-0.0009 (syst), lambda0 = 0.0183+-0.0011(stat)+-0.0006(syst), and d(lambda0)/d(lambda+)=-0.348. The limits on the possible tensor and scalar couplings have been derived: fT/f+(0)=-0.0007 +- 0.0071, fS/f+(0)=0.0017 +- 0.0014. No visible non-linearity in the form-factors have been observed.
The decay $K^{-} to mu^{-} bar{ u} pi^{0}$ has been studied using in-flight decays detected with ``ISTRA+ setup operating in the 25 GeV negative secondary beam of the U-70 PS. About 112K events were used for the analysis. The $lambda_{+}$ and $lambda_{0}$ slope parameters of the decay formfactors $f_{+}(t)$, $f_{0}(t)$ have been measured : $lambda_{+}= 0.0321 pm 0.004$(stat) $pm 0.002$(syst) $lambda_{0}= 0.0209 pm 0.004$(stat) $pm 0.002$(syst); the correlation $d lambda_{0}/d lambda_{+}=-0.46$ The limits on the possible tensor and scalar couplings have been derived: $f_{T}/f_{+}(0)=-0.021 pm 0.028$(stat) $pm 0.014$(theory); $f_{S}/f_{+}(0)=0.004 pm 0.005$(stat) $pm 0.005$(theory)
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.
The recent progress in search for T-violating transverse muon polarization in the decays K^+ --> pi^0 mu^+ nu and K^+ --> mu^+ nu gamma in the on-going experiment E246 at KEK is reported. Future prospects in polarization measurements are also discussed.
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