Performance of gas electron tracking detectors for beta decay studies

At the low-energy frontier, among the experiments testing the Standard Model and searching for new physics, are precision spectrum shape and correlation coefficient measurements in nuclear and neutron beta decay. For identification and 3D-tracking of low-energy electrons, a special type of gas-based detector was designed that minimizes scattering and energy loss. First, the newly developed gas tracker was successfully used to study tiny effects in the beta spectrum shape for allowed Gamow-Teller transitions. The miniBETA spectrometer consists of a hexagonally structured multi-wire drift chamber (MWDC) filled with a mixture of helium and isobutane gas and a plastic scintillator serving as a trigger source and energy detector. The drift time information is used to establish the electron tracks in the plane perpendicular to the wires, while the charge division technique provides spatial information along the wires. Second, inspired by the performance of this spectrometer we are building a Mott polarimeter to be used in the BRAND experiment to study the neutron decay correlation coefficients.