Deuteron-to-Proton Mass Ratio from Simultaneous Measurement of the Cyclotron Frequencies of H2+ and D+

By simultaneously measuring the cyclotron frequencies of an H-2(+) ion and a deuteron in a coupled magnetron orbit we have made an extended series of measurements of their cyclotron frequency ratio. From the observed changes in H-2(+) mass energy we have followed the decay of three ions to the vibrational ground state. We are able to assign some of our measured ratios to specific rovibrational levels, hence reducing uncertainty due to H-2(+) rotational energy. Assuming the most probable assignment, we obtain a deuteron-to-proton mass ratio, m(d)/m(p) = 1.999 007 501 272(9). Combined with the atomic mass of the deuteron [S. Rau et al., Nature (London) 585, 43 (2020).] we also obtain a new value for the atomic mass of the proton, m(p) = 1.007 276 466 574(10) u.

Automated summary

By measuring the cyclotron frequencies of H-2(+) ions and deuterons simultaneously, the decay process to the vibrational ground state was tracked, leading to a new value for the atomic mass of the proton.