Study of induced matrix elements in beta decay with a multiwire drift chamber based spectometer

Measurements of correlation coefficients between spin and momentum vectors of the particles produced in nuclear beta decay provide a sensitive means to search for physics beyond the Standard Model and test fundamental symmetries of the weak interaction. Over the last decade several new experiments have been set up and others are being prepared. Our group is actively involved in this, with two experimental methods, i.e. the WITCH Penning trap based experiment for beta-neutrino correlation measurements and a method to determine the beta-asymmetry parameter in the decay of polarized nuclei. New, precise results have recently been obtained by several groups, including our own. At the current level of precision (i.e. of the order of 0.5%) the so-called recoil effects, related to the fact that the decaying quark couples to the weak field as a bound particle and not as a free quark, have to be taken into account in order to obtain the best possible sensitivity to new physics. The largest of these is the so-called weak magnetism. In this project we will investigate these effects in detail. At the theoretical side the related induced matrix elements will be calculated and compared to experimental results. At the experimental side a new beta spectrometer will be developed allowing to determine the size of the recoil effects directly. This compact miniBETA. spectrometer will combine a multi-wire drift chamber for the tracking of beta particles with energy sensitive detectors for determining their energy.

Keywords:Beta-neutrino correlation, Beta asymmetry, Polarized nuclei, Penning ion trap, Tensor currents, Scalar currents, Beta decay, Weak interaction

Disciplines:Classical physics, Elementary particle and high energy physics, Other physical sciences