Measurement of the branching ratio of the 6He β-decay channel into the α plus d continuum

We measured the deuteron-emission branch of the beta decay of the halo nucleus He-6 using the technique of implantation into a highly segmented silicon detector. The method, used here for the first time with a beam of He-6 ions, ensures precise normalization; the value obtained for the branching ratio is B=(1.65 +/- 0.10)x10(-6) (6% error). The summed energy spectra of the emitted alpha and d particles has also been measured. The results allow us to compare calculations from various models, potentially setting strong constraints on the precision required for the description of the He-6 ground-state wave function.