Frederik Wauters

Weak interaction studies with 6He

The 6He nucleus is an ideal candidate to study the weak interaction. To this end we have built a high-intensity source of 6He delivering ∼1010 atoms/s to experiments. Taking full advantage of that available intensity we have performed a high-precision measurement of the 6He half-life that directly probes the axial part of the nuclear Hamiltonian. Currently, we are preparing a measurement of the beta-neutrino angular correlation in 6He beta decay that will allow to search for new physics beyond the Standard Model in the form of tensor currents.

Charge-state distribution of Li ions from the β decay of laser-trapped He6 atoms

The accurate determination of atomic final states following nuclear β decay plays an important role in several experiments. In particular, the charge state distributions of ions following nuclear β decay are important for determinations of the β-ν angular correlation with improved precision. Beyond the hydrogenic cases, the decay of neutral He6 presents the simplest case. Our measurement aims at providing benchmarks to test theoretical calculations. The kinematics of Lin+ ions produced following the β decay of He6 within an electric field were measured using He6 atoms in the metastable (1s2s,S13) and (1s2p,P23) states confined by a magneto-optical trap. The electron shakeoff probabilities were deduced, including their dependence on ion energy. We find significant discrepancies on the fractions of Li ions in the different charge states with respect to a recent calculation.

Laser trapped 6He as a probe of the weak interaction and a test of the sudden approximation

Synopsis Correlations between β decay products are sensitive observables to look for exotic contributions to the weak interaction excluded by the Standard Model of particle physics. To precisely measure the β − ν angular correlation parameter, a βν , in 6 He β decay, the radioactive atoms are trapped in a magneto-optical trap and the momentum of β particles and 6 Li recoil ions are measured in coincidence. The shake-off process, leading to higher charge states of the Li, plays an important role in this observation and must be studied carefully. Its study provides stringent tests of the sudden approximation for atomic calculations in this few electron system.