New Findings on Atomic Nucleus Structure and Potential Dark Forces

New Findings on Atomic Nucleus Structure and Potential Dark Forces
by Robert Schreiber
Berlin, Germany (SPX) Feb 18, 2025

For nearly a century, scientists have observed that a significant portion of the universe's matter consists of mysterious dark matter, which interacts with visible matter primarily through gravity. However, whether additional "dark forces" exist that mediate interactions between visible and dark matter remains an open question.

These forces, if they exist, should also affect atomic structures, which can now be studied with exceptional precision. "Measuring isotope shifts in electronic resonance frequencies is a particularly powerful method to explore the interaction between nuclear and electron structures," explained Tanja Mehlstaubler. Isotopes of an element differ only in the number of neutrons within their nuclei.

In 2020, researchers at the Massachusetts Institute of Technology (MIT) uncovered an unexpected nonlinearity while examining isotope shifts in ytterbium. This anomaly sparked considerable interest within the atomic physics community, prompting speculation about whether this deviation hinted at a new "dark force" or was simply an effect related to nuclear properties. The question arose: Could atomic physicists be inadvertently delving into nuclear physics by studying electron transition frequencies across isotopes?

To investigate further, Tanja Mehlstaubler from PTB in Braunschweig and Klaus Blaum from MPIK in Heidelberg led research teams that conducted high-precision measurements of atomic transition frequencies and isotope mass ratios in ytterbium isotopes. PTB utilized linear high-frequency ion traps and ultra-stable laser systems for optical spectroscopy, while isotope mass ratios were determined at MPIK using the PENTATRAP Penning trap mass spectrometer. These experiments achieved accuracy levels up to 100 times greater than previous studies.

Their findings confirmed the previously observed anomaly, but thanks to new nuclear theory calculations by Achim Schwenk's group at TU Darmstadt, an explanation emerged. The collaboration, which included theoretical atomic physicists from MPIK in Heidelberg, the University of New South Wales in Sydney, and particle physicists from Leibniz University Hannover, established new constraints on the possible existence of dark forces.

Moreover, the study provided direct insight into the deformation of atomic nuclei along the ytterbium isotope chain, contributing valuable information about the structure of heavy atomic nuclei and neutron-rich matter. This knowledge is fundamental to understanding neutron stars and the behavior of dense astrophysical objects.

This research underscores the growing synergy between atomic, nuclear, and particle physics in the quest for new physics. It also paves the way for deeper insights into the fundamental forces shaping matter.

Research Report:Probing new bosons and nuclear structure with ytterbium isotope shifts.