Precision measurements in 20f beta decay

The beta decay of 20F is an attractive low-energy probe for new physics. A parameter in beta decay highly sensitive to interactions beyond the standard model is the Fierz term. Since 20F is a Gamow-Teller decay, the Fierz term corresponds to tensor couplings in weak interactions. A beta spectrum shape measurement was done to measure the Fierz term in 20F. The analysis is not yet completed but a preliminary result is presented here. The current value of the Fierz term obtained is 0:0021 0:0051stat 0:0084sys.In addition to the shape measurement, a half-life measurement was done. Previous measurements were inconsistent. The half-life was measured as 11:0011 0:0069stat 0:0030sys s. This is the most precise measurement of the half-life of 20F, and is 17 standard deviations away from the previously adopted value. This result has been conrmed by an additional measurement from another group using a dierent technique.