High-accuracy laser spectroscopy of <math xmlns="http://www.w3.org/1998/Math/MathML"> <msubsup><mrow><mi>H</mi></mrow> <mrow><mn>2</mn></mrow> <mrow><mi>+</mi></mrow> </msubsup> </math> and the proton-electron mass ratio.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 40770440.
- Also identified by DOI 10.1038/s41586-025-09306-2 and PMC identifier 12328222.
- Licence recorded as CC BY.
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Abstract
The molecular hydrogen ions (MHI) are three-body systems suitable for advancing our knowledge in several domains: fundamental constants, tests of quantum physics, search for new interparticle forces, tests of the weak equivalence principle<sup>1</sup> and, once the anti-molecule <math xmlns="http://www.w3.org/1998/Math/MathML"> <mrow> <mover><mrow><mi>p</mi></mrow> <mo>¯</mo></mover> <mspace></mspace> <mover><mrow><mi>p</mi></mrow> <mo>¯</mo></mover> <mspace></mspace> <msup><mrow><mi>e</mi></mrow> <mrow><mo>+</mo></mrow> </msup> </mrow> </math> becomes available, new tests of charge-parity-time-reversal invariance and local position invariance<sup>1-3</sup>. To achieve these goals, high-accuracy laser spectroscopy of several isotopologues, in particular <math xmlns="http://www.w3.org/1998/Math/MathML"> <msubsup><mrow><mi>H</mi></mrow> <mrow><mn>2</mn></mrow> <mrow><mo>+</mo></mrow> </msubsup> </math> , is required<sup>4</sup>. Here we present a Doppler-free laser spectroscopy of a <math xmlns="http://www.w3.org/1998/Math/MathML"> <msubsup><mrow><mi>H</mi></mrow> <mrow><mn>2</mn></mrow> <mrow><mo>+</mo></mrow> </msubsup> </math> rovibrational transition, achieving line resolutions as large as 2.2 × 10<sup>13</sup>. We accurately determine the transition frequency with 8 × 10<sup>-12</sup> fractional uncertainty. We also determine the spin-rotation coupling coefficient with 0.1 kHz uncertainty and its value is consistent with the state-of-the-art theory prediction<sup>5</sup>. The combination of our theoretical and experimental <math xmlns="http://www.w3.org/1998/Math/MathML"> <msubsup><mrow><mi>H</mi></mrow> <mrow><mn>2</mn></mrow> <mrow><mo>+</mo></mrow> </msubsup> </math> data allows us to deduce a new value for the proton-electron mass ratio m<sub>p</sub>/m<sub>e</sub>. It is in agreement with the value obtained from mass spectrometry and has 2.3 times lower uncertainty. From combined MHI, H/D and muonic H/D data, we determine the baryon mass ratio m<sub>d</sub>/m<sub>p</sub> with 1.1 × 10<sup>-10</sup> absolute uncertainty. The value agrees with the directly measured mass ratio<sup>6</sup>. Finally, we present a match between a theoretical prediction and an experimental result, with a fractional uncertainty of 8.1 × 10<sup>-12</sup>. Both results indicate a notable confirmation of the predictive power of quantum theory and the absence of beyond-the-standard-model effects at these levels.