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HK: Hadronen und Kerne

HK 21: Weak Interaction and Fundamental Symmetries I

HK 21.1: Talk

Monday, March 16, 1998, 17:00–17:15, J

Measurement of the decay parameters in the decay of free neutrons — •Hartmut Abele¹, Margarita Astruc Hoffmann¹, Stefan Bae"sler¹, Philipp von B"ulow¹, Dirk Dubbers¹, Valeri Nesvizhevsky², Uta Peschke¹, J"urgen Reich¹, and Oliver Zimmer² — ¹Physikalisches Institut, Universit"at Heidelberg, Philosophenweg 12, D-69120 Heidelberg — ²Institut Laue - Langevin, Avenue des Martyrs, F-38042 Grenoble

The spectrometer PERKEO II was designed to measure neutron decay correlation coefficients. Here we present a new measurement of the beta asymmetry coefficient A. This coefficient allows us (together with a neutron lifetime measurement) to deduce the weak coupling constants from neutron decay alone. A precise knowledge of these coupling constants probes the structure of the electroweak standard model at low energies. Further, all semileptonic cross-sections used in cosmology, astrophysics and particle physics are based on these neutron decay data. Our value for A differs by three standard deviations from the value adopted by the particle data group in 1996.