WITCH: a recoil spectrometer for weak interaction and nuclear physics studies

Abstract

An experimental set-up is described for the precise measurement of the recoil energy spectrum of the daughter ions from nuclear beta decay. The experiment is called WITCH, short for Weak Interaction Trap for CHarged particles, and is set up at the ISOLDE facility at CERN. The principle of the experiment and its realization are explained as well as the main physics goal. A cloud of radioactive ions stored in a Penning trap serves as the source for the WITCH experiment, leading to the minimization of scattering and energy loss of the decay products. The energy spectrum of the recoiling daughter ions from the ¬-decays in this ion cloud will be measured with a retardation spectrometer. The principal aim of the WITCH experiment is to study the electroweak interaction by determining the beta-neutrino angular correlation in nuclear ¬-decay from the shape of this recoil energy spectrum. This will be the first time that the recoil energy spectrum of the daughter ions from ¬-decay can be measured for a wide variety of isotopes, independent of their specific properties. IntroductionThe standard model of the electroweak interaction is very successful in describing the interaction both qualitatively and quantitatively. However, it contains many free parameters and ad hoc assumptions. One of these is that from the five possible types of weak interactionsvector (V), axial-vector (A), scalar (S), tensor (T) and pseudoscalar interaction (P) -just V and A interactions are present at a fundamental level. Together with maximal parity violation this has led to the well known V A structure of the weak interaction. Most experimental limits for the S and T coupling constants in the charged current sector are rather weak, though [1,2,3,4],

Prospects for precision measurements in nuclear decay in the LHC era

“…Another experiment aiming at meassuring a in 35 Ar decay is the Weak Interaction Trap for CHarged particles spectrometer (WITCH) at ISOLDE-CERN [71]. The setup includes two Penning traps located in the same magnetic field.…”

“…Comparable levels of precision are currently being reached by new measurements [69] or have been anticipated by ongoing projects [71]. It appears challenging that the new round of measurements of a would be able to improve the bounds on scalar couplings set by the Fierz term extracted from the F t-values in pure Fermi transitions, Eq.…”

First high-statistics and high-resolution recoil-ion data from the WITCH retardation spectrometer

“…The conditions present in atom and ion traps reduce the effects of scattering of the β particles and recoil ions, which is a limitation when sources are implanted in materials. Whereas most β-ν correlation experiments measure coincidences between the recoil ions and the β particles to infer the neutrino momenta, the Weak Interaction Trap for CHarged particles (WITCH) experiment [19][20][21][22][23][24][25], situated at CERN-ISOLDE [26], uses a double Penning trap and retardation spectrometer ( fig. 1) to measure the energy spectrum of the recoiling daughter nuclei, in singles.…”

Axisymmetric Magnetic Field Calculation With Zonal Harmonic Expansion

“…A special kind of electron and ion energy spectroscopy is realized by the MAC-E filter spectrometers, where integral energy spectrum is measured by the combination of electrostatic retardation and magnetic adiabatic collimation. Examples are the Mainz and Troitsk electron spectrometers [4,5], the aSPECT proton spectrometer [6,7], the WITCH ion spectrometer [8,9], and the KATRIN pre-and main electron spectrometers [10].…”