Speaker
Description
The comparison of bound-state energy spectra of hydrogen and antihydrogen constitutes a stringent test of fundamental symmetry such as Lorentz and CPT invariance [1]. The availability of excitable transitions in combination with frequency metrology can be harnessed for precision measurements of energy intervals in both matter and antimatter species. The precisely determined energy spectra and a theoretically tractable structure allow for a straightforward interpretation of results. Since hydrogen and antihydrogen are charge neutral, effects from environmental noise are reduced, and motion under the influence of gravity can be studied despite the small effects arising in laboratory conditions on Earth. Here, the comparison of behaviour between the matter and antimatter species constitutes a test of the Weak Equivalence Principle.
In this presentation I will review the progress of antihydrogen studies in the Antimatter Factory at CERN. The field has been transformed from initial proof-of-principle synthesis and trapping of antihydrogen to precision measurements. This transformation is underpinned by the new ELENA source of low energy antiprotons [2], the production of substantial samples of anti-atoms by sympathetic cooling with laser cooled beryllium ions [3], laser cooling of antihydrogen [4], and the integration of a primary frequency reference [5] in the ALPHA experiment at CERN. The hyperfine components of the 1S-2S two-photon transition in trapped antihydrogen can now be measured in one day [6] and the effect of gravity on the motion of antimatter has been observed [7]. I will present the most recent results and an outlook of antihydrogen spectroscopy and gravitational studies. I will conclude with the prospects of the synthesis and ultraprecise spectroscopy of antihydrogen molecular ions for future improvements of fundamental symmetry tests.
[1] M. Charlton, S. Eriksson, G. M. Shore, Antihydrogen and Fundamental Physics (Springer Cham, 2020) (https://arxiv.org/abs/2002.09348).
[2] C. Carli et al, ELENA: Bright Perspectives for Low Energy Antiproton Physics, Nuclear Physics News 32 21 (2022).
[3] R. Akbari et al. (ALPHA Collaboration), Be+ assisted accumulation of more than 15000 antihydrogen atoms. Nature Communications 16 10106 (2025).
[4] C. J. Baker et al. (ALPHA Collaboration), Laser cooling of antihydrogen atoms. Nature 592, 35-42 (2021).
[5] J. Nauta et al. Evaluation of a caesium fountain frequency standard for antihydrogen spectroscopy Metrologia 62 045008 (2025).
[6] C. J. Baker et al. (ALPHA Collaboration), Precision spectroscopy of the hyperfine components of the 1S–2S transition in antihydrogen. Nature Physics 21 201 (2025).
[7] E. K. Anderson et al. (ALPHA collaboration), Observation of the effect of gravity on the motion of antimatter, Nature 621 717 (2023).
| Theoretical or experimental | Experimental |
|---|