Weak interaction physics at ISOLDE

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 V ud 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. In addition, new projects respectively searching for scalar currents in the β-delayed proton decay of 32 Ar, or to determine the V ud quark-mixing matrix element from the β-asymmetry parameter in the mirror decay of 35 Ar, have just started.

New physics searches in nuclear and neutron β decay

“…A project with the same aim, called WISARD, is being prepared at ISOLDE [79,177]. There the superconducting magnet system of the former WITCH project [332] will be used to provide a large solid angle to detect the β particles and protons from the 32 Ar mother isotopes.…”

“…Rings of β and proton detectors are envisaged to record the decay products. A precision of 0.1% on the β-ν correlation coefficient is aimed at [79].…”

Investigating Shakeoff Process in Precise Correlation Measurements in Nuclear β Decay

“…Since neutrinos are difficult to detect, sensitive observables for  angular correlation measurements are kinematic parameters affected by the recoiling daughter nucleus motion. Two methods are commonly used: (i) a direct method in which either the recoil energy distribution [2] or the recoil ion time of flight (ToF) distribution thanks to its detection in coincidence with the  particle [3], is measured or (ii) an indirect method in which the Doppler shift of a delayed particle ( or p) emitted during the recoil motion [4][5][6] is measured. The direct method requires the use of very clean radioactive sources, ideally placed in vacuum, due to the very low recoil kinetic energy (~ 1-2 keV at most).…”

“…This spectrometer makes LPCTrap a unique and unprecedented setup for the measurement of charge-state distributions of ions associated to the  decay of singly charged radioactive ions. The performances of the whole setup for experiments performed with 6 He, 35 Ar and 19 Ne are given in [14].…”

“…Figure 1 shows the recoil ion ToF distribution measured at GANIL using LPCTrap. A total of 1.2×10 6 final coincidences has been collected and analyzed with realistic simulations including all the identified systematic effects [15]. The induced corrections and systematic uncertainties are summarized in Table 1.…”