Proton-electron mass ratio from laser spectroscopy of HD+ at the part-per-trillion level

Sayan Patra, M. Germann, J. Ph Karr, M. Haidar, L. Hilico, V. I. Korobov, F. M.J. Cozijn, K. S.E. Eikema, W. Ubachs, J. C.J. Koelemeij

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Recent mass measurements of light atomic nuclei in Penning traps have indicated possible inconsistencies in closely related physical constants such as the proton-electron and deuteron-proton mass ratios. These quantities also influence the predicted vibrational spectrum of the deuterated molecular hydrogen ion (HD+) in its electronic ground state. We used Doppler-free two-photon laser spectroscopy to measure the frequency of the v = 0→9 overtone transition (v, vibrational quantum number) of this spectrum with an uncertainty of 2.9 parts per trillion. By leveraging high-precision ab initio calculations, we converted our measurement to tight constraints on the proton-electron and deuteron-proton mass ratios, consistent with the most recent Penning trap determinations of these quantities. This results in a precision of 21 parts per trillion for the value of the proton-electron mass ratio.

Original languageEnglish
Pages (from-to)1238-1241
Number of pages4
JournalScience (New York, N.Y.)
Issue number6508
Publication statusPublished - 4 Sept 2020


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