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Register a new userPrecise Measurement of pi+ -> e+ nu Branching Ratio
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E. Frlev{z}
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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.
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A new measurement of $B_{pi e2}$, the $pi^+ to e^+ u(gamma)$ decay branching ratio, is currently under way at the Paul Scherrer Institute. The present experimental result on $B_{pi e2}$ constitutes the most accurate test of lepton universality available. The accuracy, however, still lags behind the theoretical precision by over an order of magnitude. Because of the large helicity suppression of the $pi_{e2}$ decay, its branching ratio is susceptible to significant contributions from new physics, making this decay a particularly suitable subject of study.
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.
Three events for the decay K+ => pi+,nu,nubar have been observed in the pion momentum region below the K+ => pi+,pi0 peak, 140 < P_pi < 199 MeV/c, with an estimated background of 0.93+-0.17(stat.)+0.32-0.24(syst.) events. Combining this observation with previously reported results yields a branching ratio of B(K+ => pi+,nu,nubar) = (1.73+1.15-1.05)e-10 consistent with the standard model prediction.
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.
E865 at the Brookhaven National Laboratory AGS collected about 70,000 K+(e3) events to measure the K+(e3) branching ratio relative to the observed K+ -> pi+ pi0, K+ -> pi0 mu+ nu, and K+ -> pi+ pi0 decays. The pi0 in all the decays was detected using the e+e- pair from pi0 -> e+e-gamma decay and no photons were required. Using the Particle Data Group branching ratios for the normalization decays we obtain BR(K+(e3(gamma))=(5.13+/-0.02(stat)+/-0.09(sys)+/-0.04(norm))%, where $K+(e3(gamma)) includes the effect of virtual and real photons. This result is 2.3 sigma higher than the current Particle Data Group value. The implications of this result for the $V_{us}$ element of the CKM matrix, and the matrixs unitarity are discussed.
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