The β-asymmetry parameter A for the Gamow-Teller decay of 60Co was measured by polarizing the radioactive nuclei with the brute force low-temperature nuclear-orientation method. The 60Co activity was cooled down to milliKelvin temperatures in a 3He-4He dilution refrigerator in an external 13 T magnetic field. The β particles were observed by a 500 μm thick Si PIN diode operating at a temperature of about 10 K in a magnetic field of 0.6 T. Extensive GEANT4 Monte-Carlo simulations were performed to gain control over the systematic effects. Our result, A=−1.014(12)stat(16)syst, is in agreement with the Standard-Model value of −0.987(9), which includes recoil-order corrections that were addressed for the first time for this isotope. Further, it enables limits to be placed on possible tensor-type charged weak currents as well as other physics beyond the Standard Model.
@article{arxiv.1005.5034,
title = {Precision measurements of the $^{60}$Co $\beta$-asymmetry parameter in search for tensor currents in weak interactions},
author = {F. Wauters and I. S. Kraev and D. Zákoucký and M. Beck and M. Breitenfeldt and V. De Leebeeck and V. V. Golovko and V. Yu. Kozlov and T. Phalet and S. Roccia and G. Soti and M. Tandecki and I. S. Towner and E. Traykov and S. Van Gorp and N. Severijns},
journal= {arXiv preprint arXiv:1005.5034},
year = {2010}
}