Proton-Electron Mass Ratio from Laser Spectroscopy of HD$^+$ at the Part-Per-Trillion Level

TL;DR

This paper reports a highly precise laser spectroscopy measurement of HD$^+$ that constrains the proton-electron mass ratio with unprecedented accuracy, helping to resolve discrepancies in fundamental particle mass measurements.

Contribution

It introduces a novel high-precision measurement of the vibrational spectrum of HD$^+$, leading to a new, highly accurate value of the proton-electron mass ratio.

Findings

Proton-electron mass ratio determined with 21 parts-per-trillion precision.

Measurement aligns with recent Penning-trap results.

Demonstrates the effectiveness of Doppler-free two-photon spectroscopy for fundamental constants.

Abstract

Accepted values of the masses of several subatomic particles have been under debate since recent measurements in Penning traps produced more precise yet incompatible results, implying possible inconsistencies in closely related physical constants like the proton-electron and deuteron-proton mass ratios. These quantities also influence the predicted vibrational spectrum of the deuterated molecular hydrogen ion in its electronic ground state, of which we measured the v=0 - 9 overtone transition frequency with an uncertainty of 2.9 parts-per-trillion through Doppler-free two-photon laser spectroscopy. Leveraging high-precision ab initio calculations we convert 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, and yielding a new value of the proton-electron mass ratio with an unprecedented precision of 21 parts-per-trillion.