High-precision Penning-trap Measurement of the Helium-3 Atomic Mass

Abstract

This work presents a high-precision atomic mass measurement of helium-3. The measurement was performed using the Penning-trap mass spectrometer Liontrap, where the cyclotron frequency of the helium ion was measured relative to that of a carbon ion, which serves as a standard in atomic mass units. With a relative uncertainty of 1.2 × 10−11, this result represents the most precise mass measurement of helium-3 in atomic mass units to date. It contributes to resolving the “Light Ion Mass Puzzle” - inconsistencies in the measured masses of light nuclei, namely the proton, deuteron, and helium-3, reported by different Penning-trap mass spectrometers in the past. By demonstrating consistency between the results from Liontrap and those from the group at Florida State University, while simultaneously highlighting a discrepancy with the results from the University of Washington (UW), this work suggests that the earlier Penning-trap measurements by the UW group may have underestimated the uncertainty in their results. Consequently, confidence in Penning-trap measurements of light ion masses - fundamental constants used to test the validity of the Standard Model - is restored. During the course of this work, the experimental setup was upgraded to allow for the production of helium-3 ions and an improved detection system. Additionally, a new analysis approach was introduced, which effectively suppresses the dominant systematic effect observed in previous Liontrap measurements, the lineshape effect, by a factor of more than 100. Furthermore, a phase-sensitive method for measuring the axial frequency has been developed, showing promising potential for improving the statistical precision achievable in Penning-trap experiments in general. The measurement presented in this thesis concludes a series of studies on light ions conducted at Liontrap, and the experimental setup is now being repurposed for lepton symmetry tests at MPIK