Precision measurement of the mass difference between tritium and helium-3*

The KATRIN tritium beta-decay neutrino mass experiment has already reduced the limit on effective electron neutrino mass to 0.8 eV/c² (90% C.L), with an eventual aim of 0.2 eV/c² [1]. Using the novel method of cyclotron radiation emission spectroscopy, which inherently provides absolute electron energy calibration, the Project-8 collaboration aims to reach an eventual sensitivity of 0.04 eV/c² [2].  Comparing the value for the endpoint of the electron spectrum with a Q-value determined independently from the mass difference between tritium and helium-3 provides a test of systematics in these experiments. Here, improving on our previous measurement [3], we present results of a new precision Penning trap measurement of the mass difference between tritium and helium-3, obtained by measuring the cyclotron frequency ratios HD⁺/³He⁺, HD⁺/T⁺ and T⁺/³He⁺, each with an uncertainty of less than 10 parts-per-trillion.

[1] M. Aker et al, KATRIN Collaboration, Nature Physics 18, 160 (2023).

[2] A. Ashtari Esfahini, et al, (Project-8 collaboration], arXiv:2212.05048v1 (2022).

[3] E. G. Myers, A. Wagner, H. Kracke and B. A. Wesson, Phys Rev. Lett. 114, 013003 (2015).