Event detection in Project 8 : Detection efficiency and its implications for the first tritium β-decay spectrum recorded with Cyclotron Radiation Emission Spectroscopy

Abstract

The Project 8 collaboration aims to measure the absolute antineutrino mass scale from the shape of the tritium β-decay spectrum near its endpoint. To this end, the collaboration has successfully established Cyclotron Radiation Emission Spectroscopy (CRES), a new frequency-based approach to detect electrons and determine their kinetic energy. The CRES event signal consists of a sudden onset of narrow-band power persisting for a short amount of time. In this thesis, an event detection system consisting of real-time triggering and offline event reconstruction has been developed. This system searches for the characteristic signal features in the continuously digitized and processed radio-frequency signal. Reconstructing the initial frequency of each electron event makes it possible to record a decay spectrum with high precision. Since the mass of the electron antineutrino is determined from the shape distortion it induces in the tritium spectrum near the high-energy endpoint, it is essential to quantify any dependence of the electron detection efficiency on energy or, equivalently, frequency. In this work, the detection efficiency has been measured and the importance of including it in the analysis for an accurate determination of the endpoint and the extraction of the antineutrino mass has been demonstrated. In addition, the efficiency uncertainty has been propagated in the analysis of the first tritium spectrum recorded with CRES and a precision requirement for a future CRES experiment with a 40 meV target sensitivity to the antineutrino mass has been determined.