Abstract
Radioactive nuclei offer unique possibilities to study the structure and symmetries of the weak interaction in nuclear β decay. The large variety of nuclear states available allows selecting the ones that are best suited to study the phenomena of interest with optimal sensitivity, while at the same time minimising the effects of nuclear structure. The ISOLDE facility, offering worldwide the largest variety and intensity of radioactive beams, is one of the best suited laboratories in this respect. Over the last decade or so different aspects of the weak interaction have been studied at ISOLDE, ranging from half-lives, branching ratios and nuclear masses relevant for the determination of the Vud quark-mixing matrix element, over β-asymmetry and correlation measurements searching for possible tensor and/or scalar contributions to the weak interaction, up to a measurement showing the effect of parity violation in the weak interaction in gamma decay. In addition, new projects respectively searching for scalar currents in the β-delayed proton decay of 32Ar, or to determine the Vud quark-mixing matrix element from the β-asymmetry parameter in the mirror decay of 35Ar, have just started.
Highlights
Over the last decade or so different aspects of the weak interaction have been studied at ISOLDE, ranging from half-lives, branching ratios and nuclear masses relevant for the determination of the Vud quark-mixing matrix element, over β-asymmetry and bn correlation measurements searching for possible tensor and/or scalar contributions to the weak interaction, up to a measurement showing the effect of parity violation in the weak interaction in gamma decay
New projects respectively searching for scalar currents in the β-delayed proton decay of 32Ar, or to determine the Vud quark-mixing matrix element from the β-asymmetry parameter in the mirror decay of 35Ar, have just started
Depending on the nuclei which will be considered for future measurements of this parameter, measurements of Q value, half-life and branching ratio could be envisaged at ISOLDE
Summary
Nuclear beta decay has made some very important contributions to our present understanding of the weak interaction, for example establishing the violation of parity [1, 2], the helicity of. Recent experiments at ISOLDE have contributed to many aspects of probing the properties of the weak interaction: (i) precision decay spectroscopy on super-allowed pure Fermi decays [5] and mirror β transitions [37, 38], as well as high-precision mass measurements taking advantage of the excellent (up to the 10−9 level) precision that can be reached with Penning trap based mass spectrometers [32] such as ISOLTRAP [39], have been performed, all contributing to the determination of the Vud quark-mixing matrix element, (ii) a measurement of the beta emission asymmetry parameter in the decay of 67Cu [36] polarised with the low-temperature nuclear orientation method [40, 41] was performed, providing information on the possible presence of a tensor type contribution to the weak interaction, while (iii) the WITCH experiment has been trying to search for a scalar type contribution [42,43,44], and (iv) a measurement of the anisotropy of γ rays in the decay of oriented 180mHf [45] has confirmed and extended the evidence for parity violation in the γ decay of this isomeric state. A series of other experiments is ongoing or being set up, for example a measurement of the β-asymmetry parameter in the decay of collinear laser beam polarised 35Ar [46], and of the bn correlation in the β-delayed proton decay of 32Ar [48]
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