The WITCH experiment has been set up for investigation of the weak interaction focussing on the b-n angular correlation coefficient a. This is determined by measuring the recoil energy distribution of daughter nuclei after b decay. A precision experiment with e.g. 35Ar will set new limits for a scalar contribution to weak interaction.
The experiment is situated behind REXTRAP in the ISOLDE hall. It consists of a double Penning trap system (to provide a cooled and scattering-free source), which is coupled to a retardation spectrometer for analysis of the recoil-ion energy-distribution. After taking data in the years 2011 and 2012 the long shut down is used for data analysis and study of systematics of the WITCH experiment.