High-Precision Mass Measurements of Light Atomic Nuclei: The Helium-4 Atomic Mass

Atomic masses with high-precision can be obtained by Penning-trap mass spectrometry. The LIONTRAP experiment is one such high-precision mass spectrometer that can achieve relative mass uncertainties of the order of 10−12 and is dedicated to light ions. The results at LIONTRAP include the atomic mass measurements of the proton [1], the deuteron and the HD+ molecular ion [2]. The deuteron mass was measured to a relative precision of 8.5 ppt [2]. Our results show an excellent agreement with values that were extracted from laser spectroscopy of HD+ [3]. This comparison is currently limited by the precision of the electron’s mass in atomic mass units (amu), derived from a measurement of the bound electron g-factor in 12C5+ [4]. 4He is a prime candidate for future improvement, as it is far less sensitive to higher-order terms of quantum electrodynamics (QED) and to the charge radius of the nucleus. Currently, we are measuring the atomic mass of 4He to support such a determination of the electron mass in amu. Moreover, the atomic mass measurements of the 4He nucleus in the past showed a discrepancy between each other.
Furthermore, an ultra-precise measurement of the mass difference of 3He and 3T will provide an important crosscheck of the systematics in the determination of the electron anti-neutrino mass with the KATRIN experiment [5]. Additionally, 3He to 12C mass ratio could further clarify the so-called ‘puzzle of the light masses’, which is an inconsistency in the values of light masses from different world-leading experiments [2]. In this contribution, the present status of the experiment will be discussed.
[1] F. Heise et al., Phys. Rev. A 100, (2019).
[2] S. Rau et al., Nature 585, (2020) pp. 43-47.
[3] I. V. Kortunov et al., Nature Physics, 17, (2021) pp. 569-573.
[4] S. Sturm et al., Nature 506, (2014) pp. 467-470.
[5] KATRIN Collaboration, Nature Physics, 18, (2022) pp. 160-166.