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2 results on '"pion beta decay"'

1. Precise measurement of the Pi+ -> Pi0 e+nu branching ratio

Author

Počanić, Dinko, Frlež, Emil, Baranov, V.A., Bertl, W., Bronnimann, Ch., Bychkov, M.: Crawford, J.F., Daum, M., Khomutov, N.V., Korenchenko, A.S., Korenchenko, S.M., Kozlowski, T., Kravchuk, N.P., Kuchinsky, N.A., Li, W., Minehart, R.C., Mzhavia, D., Ritchie, B.G., Ritt, S., Rozhdestvensky, A.M., Sidorkin, V.V., Smith, L.C., Supek, Ivan, Tsamalaidze, Z., VanDevender, B.A., Wang, Y., Wirtz, H.-P., and Ziock, K.O.H.

Subjects
pion beta decay, branching ratio, Standard Model, High Energy Physics::Experiment, Nuclear Experiment
Abstract

Using a large acceptance calorimeter and a stopped pion beam we have made a precise measurement of the rare Pi+ --> Pi0 e+ nu decay branching ratio. We have evaluated the branching ratio by normalizing the number of observed pion beta decays to the number of observed Pi+ --> e+ nu decays. We find the value of Gama(Pi+ --> Pi0 e+ nu)/Gama (total) = [1:036 +/- 0:004 (stat:) +/- 0:004 (syst:) +/- 0:003 ] x10-8, where the first uncertainty is statistical, the second systematic, and the third is the Pi+ -> e+ nu branching ratio uncertainty. Our result agrees well with the Standard Model prediction.

Published
2004

2. Precise measurement of the pion axial form factor in the pi^+ --> e^+ ni gamma decay

Author

Frlež, Emil, Počanić, Dinko, Baranov, V.A., Bertl, W., Bychkov, Khomutov, N.V., Korenchenko, A.S., Korenchenko, S.M., Kozlowski, T., Kravchuk, N.P., Kuchinsky, N.A., Li, W., Minehart, R.C., Mzhavia, D., Ritchie, B.G., Ritt, S., Rozhdestvensky, A.M., Sidorkin, V.V., Smith, L.C., Supek, Ivan, Tsamalaidze, Z., VanDevender, B.A., Velicheva, E.P., Wang, Y., Wirtz, H.-P., and Ziock, K.O.H.

Subjects
pion beta decay, branching ratio, Standard Model
Abstract

We have studied radiative pion decays pi^+--e^+ni^gamma in three broad kinematic regions using the PIBETA detector and a stopped pion beam. Based on Dalitz distributions of 41 601 events we have evaluated absolute pi e ni^gamma branching ratios in the three regions. Minimum Ksi^2 fits to the integral and differential (Ee+, Egamma) distributions result in the axial-to-vector weak form factor ratio of gamma FA/FV = 0.443(15), or FA = 0.0115(4) with FV = 0.0259. However, deviations from standard model predictions in the high-Egamma– low-Ee+ kinematic region indicate the need for further theoretical and experimental work.

Published
2004

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