Abstract
Background: Precision measurements at low energy search for physics beyond the standard model in a way complementary to searches for new particles at colliders. In the weak sector the most general -decay Hamiltonian contains, besides vector and axial-vector terms, also scalar, tensor, and pseudoscalar terms. Current limits on the scalar and tensor coupling constants from neutron and nuclear decay are on the level of several percent.
Purpose: Extracting new information on tensor coupling constants by measuring the -asymmetry parameter in the pure Gamow-Teller decay of , thereby testing the V-A structure of the weak interaction.
Method: An iron sample foil into which the radioactive nuclei were implanted was cooled down to mK temperatures in a dilution refrigerator. An external magnetic field of 0.1 T, in combination with the internal hyperfine magnetic field, oriented the nuclei. The anisotropic radiation was observed with planar high-purity germanium detectors operating at a temperature of about 10 K. An on-line measurement of the asymmetry of was performed as well for normalization purposes. Systematic effects were investigated using geant4 simulations.
Results: The experimental value, , is in agreement with the standard model value of 0.5991(2) and is interpreted in terms of physics beyond the standard model. The limits obtained on possible tensor-type charged currents in the weak interaction Hamiltonian are (90% C.L.).
Conclusions: The obtained limits are comparable to limits from other correlation measurements in nuclear decay and contribute to further constraining tensor coupling constants.
4 More- Received 24 April 2014
DOI:https://doi.org/10.1103/PhysRevC.90.035502
©2014 American Physical Society