Tokyo, Japan – A scientist from Tokyo Metropolitan University has proposed using safety monitoring at synchrotron facilities to study the properties of dark photons, hypothetical particles proposed to explain dark matter. Calculations showed that the X-ray source at these sites and a Geiger-Muller counter behind safety shielding could be used to propose limits on how strongly dark photons interact with normal photons. The experiment would not involve a dedicated facility and can run alongside other experiments.
Experimental particle physics is often a world of enormous collaborations, multi-national funding, and dedicated sites and facilities, yielding groundbreaking triumphs such as the discovery of the Higgs boson. The community has now turned its attention to the hunt for dark matter, some of which might account for the “missing” portion of mass in the known universe eluding detection by conventional means. Dedicated experiments include the ALPS (Any Light Particle Search) Experiment in Hamburg, which involves a high-power laser being sent through a magnetic field and then a wall before detection. These so-called Light-Shining through a Wall (LSW) experiments are considered a promising avenue in the hunt for dark matter.
However, in an about-face for dedicated experiments and sites, a scientist from Tokyo Metropolitan University, Associate Professor Wen Yin, has proposed a way to look for dark matter, particularly dark photons, using standard synchrotron facilities, where powerful X-rays are directed at matter to study their properties. One of the components of synchrotron facilities, an undulator, is itself a strong source of light passing through a magnetic field. Dr. Yin proposed to combine the potential generation of dark photons in this beam and the safety shielding wall intended to block the laser to effectively run an LSW experiment. This does not require a dedicated facility and could be run concurrently with other experiments.
In keeping with the simplicity of this setup, the proposed detection for these particles was a Geiger-Muller tube, one of the simplest means of detecting radiation and a typical part of safety monitoring. Dr. Yin theoretically modelled the passage of dark photons from a synchrotron beam through optics, safety shielding, and a standard Geiger-Muller counter, generating estimates for how many dark photons might be detected if they had certain properties. Since monitoring in these facilities already shows that radiation levels are within what is safe for users, one could then infer limits on the original properties of dark photons, specifically, upper limits on the “mixing parameter” governing dark photon-normal photon interactions. Assuming a dark photon mass of between 1 and 50 electronvolts, the limit found was less than 0.00001 times the strength of the interaction between normal photons, a much more stringent limit than any other LSW experiment purely run in a laboratory in the same mass range, in a role complementary to previous experiments.
The proposal is a groundbreaking step in applying existing facilities to a wholly new field and promises to direct the hunt for dark matter down new avenues and new methodologies.
This work was supported by JSPS KAKENHI Grant Numbers 22K14029 and 23K22486, and the Tokyo Metropolitan University Grant for Young Researchers (Selective Research Fund).
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