Precision measurement of the Beta-energy spectrum in 2076He decay

Precision measurements of the β-energy spectrum in nuclear and neutron decays have a great potential to find possible signatures of new physics beyond the standard electroweak model. Such signatures would produce a distortion to the β-energy spectrum relative to the Standard Model prediction. In Gamow-Teller transitions, these distortions would indicate the presence of the exotic tensor type interactions. An interesting candidate for this study is 6He because the simplicity of its decay and other nuclear properties allow an accurate theoretical description of the spectral shape.At the National Superconducting Cyclotron Laboratory we have used a calorimetric technique for measuring the shape of the β-energy spectrum in 6He decay. The radioactive ions were implanted into the active volume of a detector; this eliminates the critical instrumental effect related to the backscattering of β particles. The goals of the experiment are to provide the first measurement of the weak magnetism form factor (bWM) in 6He decay and the first direct measurement of the Fierz interference term (bGT) in Gamow-Teller decay.This work summarizes the efforts on this experiment, focusing on the data analysis of the main systematic effects as well as the projected sensitivities to the observables. The estimates of bWM and bGT are bWM = ? ± 4.9stat ± 11sys and bGT = (? ± 3.1stat ± 4.7sys) × 10−3, where the central values of bWM and bGT will be determined in the future analysis. The predicted uncertainty of bGT satisfies the precision goal of O(10−3), a level which allows new constraints on tensor couplings beyond the Standard Model.