THE MEASUREMENT OF THE BETA-ASYMMETRY IN THE DECAY OF POLARIZED NEUTRONS

The beta-decay asymmetry parameter A was measured for the free neutron with high precision. A time projection chamber (TPC) and plastic scin tillators were used as a track and energy detector for the decay elect rons. Thus the decay volume was well defined. Electron tracks with dif ferent angle theta between the electron momentum and the neutron spin could be selected and compared with the expected cos theta distributio n. A deviation from this distribution was observed and remains unexpla ined. Using the electron track detector only to delimit the fiducial v olume and adopting the theoretically predicted cos theta distribution a value of A(0) = -0.1160 +/- 0.0015 was determined including correcti ons for recoil and weak magnetism. To our best knowledge this result i s not influenced by the observed deviation from the cos theta distribu tion of the asymmetry. From this result the ratio g(A)/g(V) = - 1.266 +/- 0.004 can be deduced within the Standard Model. Using the recent n eutron lifetime value leads to g(V) = 1.4172 (34). 10(-62) J m(3). Thi s value is in good agreement with g(V) from ft(0(+) --> 0(+)) and mu d ecay.