Researchers observe what could be the first hints of dark bosons

Extremely light and weakly interacting particles may play a crucial role in cosmology and in the ongoing search for dark matter. Unfortunately, however, these particles have so far proved very difficult to detect using existing high-energy colliders. Researchers worldwide have thus been trying to develop alternative technologies and methods that could enable the detection of these particles.

Over the past few years, collaborations between particle and atomic physicists working at different institutes worldwide have led to the development of a new technique that could be used to detect interactions between very light bosons and neutrons or electrons. Light bosons, in fact, should change the energy levels of electrons in atoms and ions, a change that could be detectable using the technique proposed by these teams of researchers.

Using this method, two different research groups (one at Aarhus University in Denmark and the other at Massachusetts Institute of Technology) recently performed experiments aimed at gathering hints of the existence of dark bosons, elusive particles that are among the most promising dark matter candidates or mediators to a dark sector. Their findings, published in Physical Review Letters, could have important implications for future dark matter experiments.

The technique used by the Aarhus team, led by Michael Drewsen, as well as by the research team at MIT led by Vladan Vuletic, essentially entails the examination of isotope shifts arranged in 4data points. If these points form a straight line, the observations are aligned with the Standard Model, which suggest that no new physics was detected. If they are not in a straight line, however, this could hint at the presence of new bosons or other physical phenomena.

Should the nonlinearity observed using this method significantly exceed the error bars set by the Standard Model, then the researchers should be able to set new bounds on the couplings and mass of the boson they may have detected. However, if it is unexpectedly large, the nonlinearity could either be associated with a boson that disturbed an electron's energy levels or with other physical phenomena predicted by the Standard Model that are also known to break the linearity of isotope shifts.

 Improved Isotope-Shift-Based Bounds on Bosons beyond the Standard Model through Measurements of the 2D3/2−2D5/2 Interval in Ca+. Physical Review Letters DOI: 10.1103/PhysRevLett.125.123003.

Evidence for nonlinear isotope shift in Yb+ search for new Boson. Physical Review Letters
DOI: 10.1103/PhysRevLett.125.123002.

Probing atomic Higgs-like forces at the precision frontier. Physical Review D(2017). DOI: 10.1103/PhysRevD.96.093001.

Probing new long-range interactions by isotope shift spectroscopy. Physical Review Letters(2018). DOI: 10.1103/PhysRevLett.120.091801.

Theoretically, interactions between particles that have never been observed before, such as bosons, and other common particles (e.g., electrons), should be reflected in a discrepancy between the transition frequencies predicted by the Standard Model and those measured in actual atoms. Even if physicists are able to collect extremely precise frequency measurements, theory-based calculations for big atoms will have such a large margin of uncertainty that they cannot be reliably compared to direct measurements.

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