Precision measurement of the 6He half-life and the weak axial current in nuclei

Background: The beta decays of H-3 and He-6 can play an important role in testing nuclearwave-function calculations and fixing low-energy constants in effective-field theory approaches. However, there exists a large discrepancy between previous measurements of the He-6 half-life. Purpose: Our measurement aims at resolving this long-standing discrepancy in the He-6 half-life and providing a reliable ft value and Gamow-Teller matrix element for comparison with theoretical ab initio calculations. Method: We measured the He-6 half-life by counting the beta-decay electrons with two scintillator detectors operating in coincidence. Results: The measured He-6 half-life is 806.89 +/- 0.11(stat-0.19syst)(+0.23) ms corresponding to a relative precision of 3 x 10(-4). Calculating the statistical rate function we determined the ft value to be 803.04(-0.23)(+ 0.26) s. Conclusions: Our result resolves the previous discrepancy by providing a higher-precision result with careful analysis of potential systematic uncertainties. The result provides a reliable basis for future precision comparisons with ab initio calculations.