The Search For Dark Matter
Cosmologists have predicted “visible” matter to comprise only 5 percent of the universe’s total energy; 26 percent is believed to be cold dark matter. It is challenging to detect this matter due to its lack of interactions with ordinary matter. This then makes it difficult to understand its precise microscopic structure. Multiple global physics programs have proposed that dark matter consists of a new type of elementary particle, an axion, and have employed numerous types of detectors on the hunt for the hypothetical particle. If axions exist, it would provide a possible solution to both the unknown nature of dark matter.4 Additionally, axions may solve the strong charge-parity (CP) problem. In an atom, the strong nuclear force that binds quarks together to form the nuclei of atoms, regulates the structure of neutrons to make them perfectly symmetrical and the opposing weak force powers nuclear decay.3 However, the magnitude of these forces differ, which is inconsistent with the charge-parity symmetry neutrons are said to have in atomic structure. If the very light and weak neutral axion exists within an atom, and it suppresses the neutron’s asymmetries, the strong nuclear force will have an equal energy to the combined energy of the weak force and dark matter, solving the CP puzzle.1
The international Baryon Antibaryon Symmetry Experiment (BASE) collaboration in Switzerland, led by the Rikagaku Kenkyūjo (RIKEN) Fundamental Symmetries Laboratory and its researchers in Switzerland, has discovered a new way to find axions. The researchers have adapted their “superconducting single antiproton detection system [...] as a sensitive dark matter antenna.” 4 Using the BASE experiment’s single antiproton detectors, the researchers are able to set new laboratory limits on coupling photons and axion-like particles (ALPs). Axions are theorized to oscillate throughout the galaxy at mass-dependent, characteristic frequencies. “In strong magnetic fields, the particles might convert into electromagnetically interacting [particles of light called] photons.”4 The converted axions cause the resonators of the extremely sensitive single particle detectors to resonate and create a detectable “sound.”4 The detectors are tuned to search for certain frequencies of light, which have corresponding axion masses.2
Frank Wilczek, an American physicist that won a Nobel Peace Prize in 2014 for his work on the strong nuclear force, says “the existence of axions [...] would point to new physics […] New kinds of antennas could be built to look for axions created in the early universe […] axions would open up a new chapter in astronomy.”2
1 Backes, K. M., Palken, D. A., Kenany, S. A., Brubaker, B. M., Cahn, S. B., Droster, A., . . . Wang, H. (2021, February 10). A quantum enhanced search for dark matter axions. Retrieved February 10, 2021, from https://www.nature.com/articles/s41586-021-03226-7
2 Conover, E. (2020). Physicists have narrowed the mass range for hypothetical dark matter axions. ScienceNews. Retrieved February 10, 2021, from https://www.sciencenews.org/article/physicists-have-narrowed-the-mass-range-for-hypothetical-dark-matter-axions.
3 Falk, D. (2020). Is Dark Matter Made of Axions?. Scientific American. Retrieved February 10, 2021, from https://www.scientificamerican.com/article/is-dark-matter-made-of-axions/.
4 RIKEN. (2021, February 4). Dark matter: A new tool in the search for axions. ScienceDaily. Retrieved February 10, 2021 from www.sciencedaily.com/releases/2021/02/210204101657.htm