Fundamental interactions

Weak-interaction studies and symmetry tests in neutral atoms and ions are used for investigating fundamental interactions and testing the standard model via, e.g., measuring Ft values and investigating specific correlations in the β-decay process as precise as possible. As these experiments strive to the highest possible precision, the systematic errors in the experimental setup have to be understood as good as possible and large statistics are of primordial importance.

Correlation measurements

By simultaneously measuring physical observables such as energy, momentum and spin of the particles involved in nuclear β-decay, either by direct or indirect methods, correlation coefficients a, b A, R, D between those observables can be determined. Because the correlation coefficients depend on the coupling strengths for the different possible weak-interaction types, being vector (V), axial vector (A), scalar (S) en tensor (T) coupling, high-precision measurements allow to test the standard model, which assumes only V- and A-type interactions and with maximal parity violation and time reversal invariance. The use of open trap structures, such as Penning, Paul, and MOT traps is an absolute requirement in order to avoid significant systematic uncertainties.

Correlation measurements
Correlation measurements 
 Correlation measurements
 Correlation measurements

Picture from N. Severijns, presented at the BriX workshop 2008, SCK•CEN, Mol, Belgium

Super-allowed decays of T=1/2 mirror transitions

It is well known that the Conserved Vector Current (CVC) hypothesis and the unitarity of the CKM matrix can be tested by using Ft values of super-allowed 0+ → 0+ Fermi transitions. Less well known, however, is that super-allowed decays of T=1/2 mirror transitions offer a potentially more sensitive probe when its Ft value is measured in combination with the ratio φ of the Gamow-Teller to Fermi amplitudes, which can be determined by correlation measurements. So far, only few cases have been studied and there is much room for improvement.

Ft0 values deduced for five mirror transitions as a function of the mass number of the mirror nuclei

 

 Ft0 values deduced for five mirror transitions as a function of the mass number of the mirror nuclei [1].

 [1] O. Naviliat-Cuncic and N. Severijns, Phys. Rev. Lett. 102 (2009) 142302 

 

Symmetry tests in neutral atoms

By performing high-precision measurements on atoms with high atomic number Z, symmetries can be tested in the electroweak interaction. High-Z atoms are more sensitive to possible new short-ranged interactions between leptons and quarks, because the overlap of electrons with the nucleus is larger. Beams from ISOL@MYRRHA would allow exploring these possibilities using state-of-the-art atomic experimental techniques. An obvious program would be the study of time reversal violation by measuring the electric dipole moment (EDM) of atoms like radium. Another possibility would be atomic parity non-conservation (APNC) experiments with francium atoms.