Theories beyond the standard model (SM) of particle physics are usually tested using high-energy colliders or space observations. However, high-precision atomic and molecular physics experiments at low energies can also be very effective.
One method is isotope-shift spectroscopy, which studies nuclear sizes in exotic isotopes. This technique can also detect shifts in atomic energy levels caused by hypothetical new particles called bosons, which interact between neutrons and electrons.
These measurements can be analyzed using the King-plot method, which combines different atomic transitions to eliminate standard uncertainties. If the King plot shows nonlinearity, it may indicate new physics or higher-order atomic and nuclear structure effects.
This technique has been used to set limits on new physics beyond the SM, like in the case of isotope shifts measured in ytterbium. However, as the precision of frequency measurements increases, uncertainties in nuclear masses become a limiting factor in distinguishing between SM effects and new physics.
Quantum physicists from PTB and MPIK in Heidelberg achieved highly accurate measurements by combining atomic and nuclear physics using two methods. With new calculations, theoretical physicists from Darmstadt and Hannover showed that measuring the electron shell of an atom can reveal how the atomic nucleus is deformed. Additionally, their precise measurements set new limits on the strength of a possible dark force between neutrons and electrons.
For nearly a century, measurements have suggested that a large portion of the universe’s matter comprises unknown dark matter, which interacts with visible matter through gravity. It is still unclear if there are “dark forces” that can interact with both visible and dark matter.
These forces should also affect atoms, which can now be analyzed precisely. Tanja Mehlstäubler explains that “measuring the shift in electronic resonances in isotopes is a powerful method to study the interaction between nuclear and electron structures.” Isotopes are different versions of an atomic element that only differ in the number of neutrons in the nucleus.
In 2020, MIT scientists found an unexpected result while studying isotope shifts in ytterbium, causing excitement among atomic physicists. Could this be evidence of a new “dark force” or something about the atomic nucleus?
Driven by these questions, Tanja Mehlstäubler from PTB and Klaus Blaum from MPIK investigated ytterbium isotope shifts. Their teams used advanced technology to measure atomic transition frequencies and isotope mass ratios with high precision. Their measurements were up to a hundred times more accurate than previous ones.
The researchers confirmed the anomaly and explained it using new nuclear theory calculations by Achim Schwenk’s group at TU Darmstadt. Working with physicists from MPIK in Heidelberg, the University of New South Wales, and Leibniz University Hannover, they established a new limit for the existence of dark forces.
The international team also used the data to get direct information about the deformation of the atomic nucleus in ytterbium isotopes. This provides new insights into the structure of heavy atomic nuclei and the physics of neutron-rich matter, which helps us understand neutron stars.
This research creates new opportunities for collaboration in atomic, nuclear, and particle physics, leading to a better understanding of the complex phenomena that determine the structure of matter.
Journal Reference:
- M. Door et al.: Opens external link in new windowProbing new bosons and nuclear structure with ytterbium isotope shifts. Physical Review Letters Vol. 134, No. 6 (2025). DOI: 10.1103/PhysRevLett.134.063002
Source: Tech Explorist
