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WITCH

Abstract

We want to search for scalar interaction in nuclear beta decay by precisely determining the electron-neutrino correlation coefficient a. Up to now a scalar contribution to the electroweak interaction is experimentally not yet excluded at the level of 10-15% (95% CL). We intend to determine a by measuring the energy spectrum of the recoiling nuclei after beta decay. For this, we are setting up a Penning trap and a retardation spectrometer which will be coupled to REXTRAP at ISOLDE/CERN. This allows a wide choice of nuclides to be investigated. For the search for scalar interaction we will investigate Fermi-decays and mirror nuclei. Most promising are ²⁶Al^m, ³⁵Ar and ⁴⁶V. At a later stage this setup will be used for other experiments, e.g. determination of Fermi to Gamow-Teller ratios for short lived nuclides and Q-value measurements.

The experiment is approved by the ISOLDE Scientific committee as test experiment P111 with 9 shifts of stable beam and 9 shifts of radioactive beam. Floor and plattform space is allocated. After more than a year of Monte Carlo simulations the design studies are in principle finished. Ordering of the components has commenced. The setup of some of the components has started at CERN.