At the Center for Axion and Precision Physics Research (CAPP) within the Institute for Basic Science (IBS), a South Korean research group recently declared the most sophisticated experimental setup yet to search for axions.
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(Top) Current exclusion limits for axion mass from both experiments and astrophysical observation. KSVZ line is the expectation for standard KSVZ axion, while DFSZ line is GUT DFSZ axion. Searching for DFSZ axions requires much higher sensitivity than KSVZ axions. IBS-CAPP axion search experiment explored axion dark matter around 1.1 GHz frequency range at DFSZ sensitivity, denoted by red. Blue denotes the ranges previously excluded by ADMX. (Bottom) IBS-CAPP axion search experiment explored axion dark matter around 1.1 GHz frequency range at DFSZ sensitivity, denoted by blue. Red denotes the axion search experiment previously conducted by ADMX. Image Credit: Institute for Basic Science
The research team has been successful in taking its first step toward the search for Dine-Fischler-Srednicki-Zhitnitskii (DFSZ) axion dark matter sourced from the Grand Unification Theory (GUT). Further, the IBS-CAPP experimental setup enabled a much greater search speed than any other axion search experiment in the world.
In the late 19th century, William Thompson, also called Lord Kelvin, falsely thought that there would be no new breakthrough in physics after 1900. Similarly, some have believed that there were no new particles to be found following the breakthrough of neutrons in the 1930s. As of today, some worry that modern theoretical physics is at a dead end.
However, this is far from the truth. Our most common model of physics, the Standard Model, has the potential to describe only 5% of the universe, with the other 95% comprising dark energy and dark matter. The present Standard Model also has limitations in describing issues like the powerful CP (charge conjugation-parity) problem.
The issue emerges from the observation that the strong force, which is explained by quantum chromodynamics (QCD), does not seem to violate CP symmetry, while the electroweak force violates CP symmetry to a small extent. This goes against the Standard Model that states that CP symmetry must be violated by the powerful force at a level that is much larger than what has been seen.
One suggested solution to the issue involves the presence of hypothetical particles known as axions, which could solve the difference between the anticipated and found levels of CP violation in the powerful force.
Axions are known to be one of the powerful candidates for dark matter. The discovery of axion dark matter is a milestone event in human history that could reveal the reality of 27% of the Universe.
At present, two different proposals for “beyond the Standard Model” exist to describe the powerful CP issue. The primary variation between the two models is that they anticipate different kinds of couplings between axions and other particles.
In the “Kim-Shifman-Vainshtein-Zakharov” (KSVZ) model, axions are mainly linked to heavy quarks, while in the “Dine-Fischler-Srednicki-Zhitnitsky” (DFSZ) model, they are linked to the Standard Model quarks and leptons through Higgs bosons.
As dark matter, axions consist of very weak (or little) interaction with ordinary matter, hence searching for them could be a difficult business. One commonly utilized method involves microwave cavity experiments.
Such experiments make use of a powerful magnetic field to convert axions (if they exist) into resonant electromagnetic waves, which are further detected with the help of a receiver. Further, the mass of the axion could be evaluated from the detected wave’s frequency.
Since axion mass is not known, physicists should expand their search and scan a large range of frequencies.
The issue is made harder in the case of seeking a DFSZ axion, which needs much greater sensitivity compared to the KSVZ axion. In microwave cavity search experiments, obtaining greater sensitivity needs exponentially higher search time, and thus searching for DFSZ axions is impossible for almost all experimental setups available at present.
Consequently, while some axion search experiments have been successful in searching for signals in the KSVZ axion sensitivity ranges, till now, the only experiment that was able to achieve the sensitivity essential to search for DFSZ axions was the ADMX (Axion Dark Matter Experiment) performed by the ADMX collaboration.
This is the reason why IBS-CAPP is the second group in the world to successfully seek axions with DFSZ sensitivity.
The IBS-CAPP team made use of a 12T magnet, which is stronger compared to the 8T magnet that was utilized by the ADMX. For the background noise to be reduced, the experiment setup was kept at close to absolute zero temperature.
Besides using a stronger magnet, the IBS-CAPP experiment made use of quantum technologies and a highly effective computational method to curate the data. This enabled the IBS-CAPP to look for DFSZ axions at 3.5 times the rate of the ADMX setup.
The new publication by the IBS-CAPP details the illustration of their new setup for the DFSZ axion search conducted from March 1st to March 18th 2022. The group was also capable of excluding axion dark matter near 4.55 µeV at DFSZ sensitivity.
Discovery of axion will allow us to understand up to 32% of the mass-energy of the universe, up from 5% offered by the current Standard Model. We plan to take advantage of the blazingly fast speed of our experimental setup to quickly search for DFSZ axions at the wide frequency ranges of 1 to 2 GHz.
Byeong Rok Ko, Research Fellow, Institute for Basic Science-Center for Axion and Precision Physics Research
It is believed that the breakthrough will support the Grand Unification Theory (GUT), which combines the three basic forces—weak, strong, and electromagnetism.
We are highly grateful for all the funding and support that the Institute for Basic Science and South Korean taxpayers provided for this project. It is thanks to them that South Korea now hosts the most advanced axion search experimental facility in the world. If axion exists, I have no doubt it will be found right here in South Korea.
Yannis Semertzidis, Director, Institute for Basic Science-Center for Axion and Precision Physics Research