A. Lindroth

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

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 β-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 β-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 β-decay can be measured for a wide variety of isotopes, independent of their specific properties.

WITCH: a recoil spectrometer for β-decay

The WITCH experiment will measure the recoil energy spectrum of the daughter ions in beta-decay. The main parts of the experiment are two Penning traps and a subsequent retardation spectrometer. The beta-decays take place in the ion cloud in the decay trap. Since the ion cloud is in vacuum and due to the cylindrical structure of the trap, the recoiling daughter ions can leave the cloud and the trap without any significant energy loss and can be energy analyzed in the retardation spectrometer. The WITCH experiment is set up foremost to study the electroweak interaction by measuring the beta-v angular correlation in nuclear beta-decay which can be inferred from the shape of the energy spectrum of the recoil ions. In the beginning the experiment will focus on pure Fermi decays which will allow to search for additional scalar coupling in the weak interaction. Since Penning traps have no restrictions regarding the element to be trapped the most suitable isotope can be picked for this purpose. The WITCH experiment is presently being set up at ISOLDE. Status and perspectives of the experiment will be presented in the following

Search for Time Reversal Violating Effects: R-Correlation Measurement in Neutron Decay

An experiment aiming at the simultaneous determination of both transversal polarization components of electrons emitted in the decay of free neutrons begins data taking using the polarized cold neutron beam (FUNSPIN) from the Swiss Neutron Spallation Source (SINQ) at the Paul-Scherrer Institute, Villigen. A non-zero value of R due to the e− polarization component, which is perpendicular to the plane spanned by the spin of the decaying neutron and the electron momentum, would signal a violation of time reversal symmetry and thus physics beyond the Standard Model. Present status of the project and the results from analysis of the first data sample will be discussed.

Physics and Present Status of the WITCH Experiment

The WITCH experiment (Weak Interaction Trap for CHarged particles) is starting measurements at the ISOLDE facility at CERN at present. It has been set up to measure the energy spectrum of the recoiling daughter ions after nuclear beta decay for precision tests of the Standard Model of weak interactions. However, many other topics of interest are accessible. In this article, the possibilities of recoil spectroscopy with the WITCH experiment are discussed, as well as the principle of the setup and its present situation.

WITCH: Testing the standard model using a β-recoil spectrometer with a trapped ion cloud as source

Abstract The combination of a zero thickness source of β radioactivity, consisting of an ion-cloud in a Penning trap, with a retardation spectrometer has for the first time allowed the construction of a set-up that can measure the β recoil spectrum of any nucleus. This opens a number of severely hampered areas of study, such as lepton angular correlations and charge state distributions after β-decay. The former allows extraction of Standard Model violating S and T contributions to the weak interaction. An overview of the set-up is given in this presentation.

Nuclear spin-lattice relaxation of Cu-62 at low temperatures in iron

The nuclear spin-lattice relaxation of {sup 62}Cu in iron has been studied with the low temperature nuclear orientation method. At temperatures ranging from 6.5 mK to about 100 mK and a magnetic field of 0.1 T the relaxation constant for {sup 62}Cu in Fe was found to be C{sub K}[{sup 62}Cu]=4.34(25)sK.

Search for Time Reversal Violation in Neutron Decay: A Measurement of the Transverse Polarization of Electrons

A non‐zero value of the R‐correlation coefficient due to the e − polarization component, perpendicular to the plane spanned by the spin of the decaying neutron and the electron momentum, would signal a violation of time reversal symmetry and thus physics beyond the Standard Model. The value of the N‐correlation coefficient, given by the transverse e − polarization component within that plane, is expected to be finite. The measurement of N serves as an important systematic check of the apparatus for the R‐measurement. The first phase of data taking has been completed. Preliminary results from a limited data sample show no deviations from the Standard Model predictions.

Progress at the WITCH experiment

The WITCH‐experiment will measure the energy spectrum of the recoiling daughter ions in beta decay to search for non‐standard scalar and tensor type interaction. To facilitate this a Penning trap is used to store the radioactive ions. Thus the recoil ions can leave the source without any energy loss and their energy can be probed by the subsequent retardation spectrometer. The experiment is being set up at present at ISOLDE/CERN. The principle and the status of the WITCH‐experiment will be presented.