An accurate atomic mass of ${}^4\mathrm{He}$ (or the alpha particle) is required for deriving the atomic mass of the electron from proposed measurements of the ground-state $g$ factor of ${}^4\mathrm{He}^{+}$. However, there is a six-standard deviation discrepancy between a recent measurement [S. Sasidharan, O. Bezrodnova, S. Rau, W. Quint, S. Sturm, and K. Blaum, Phys. Rev. Lett. 131, 093201 (2023)] and the measurement by Van Dyck et al. [R. S. Van Dyck, Jr., D. B. Pinegar, S. Van Liew, and S. L. Zafonte, Int. J. Mass Spectrom. 251, 231 (2006)], on which the current values in the Atomic Mass Evaluation and CODATA tabulation of fundamental constants are based. By measuring the cyclotron frequency ratios of ${}^4\mathrm{He}^{+}$ to ${\mathrm{D}}_2^{+}$, and of ${}^4\mathrm{He}^{+}$ to ${\mathrm{H}}_2{\mathrm{D}}^{+}$, we find the mass of ${}^4\mathrm{He}$ to be $4.00260325467\left(8\right)\mathrm{u}$, favoring the more recent value.

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• Atoms
• Ions
• Polarizability
• Penning traps