The quest to understand the enigmatic nature of dark matter has taken a significant leap forward as scientists from the international JEDI collaboration have pioneered an innovative approach to search for dark matter particles. Employing the state-of-the-art Jülich particle accelerator COSY, these researchers have presented a promising new method to explore the mysteries of dark matter based on observing a particle beam's spin polarization. This groundbreaking study brings us closer to unlocking the secrets of the invisible cosmic substance that accounts for a significant portion of our universe.
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Dark Matter: An Overview of the Invisible Enigma in the Universe
Dark matter, an invisible and enigmatic substance, comprises over 80% of the matter in the universe. Unlike visible matter, known as baryonic matter consisting of electrons, protons, and neutrons, dark matter emits no light or energy, making it undetectable by conventional means.
The nature of dark matter remains a mystery, and despite numerous theories proposed by theoretical physicists, no direct detection has been achieved. It is uncertain whether dark matter consists of baryons or non-baryonic particles, adding to its elusive nature.
Among the hypothetical candidates for dark matter are axions and axion-like particles (ALPs).
Originally, axions were intended to solve a problem in the theory of the strong interaction of quantum chromodynamics. The name axion can be traced back to the winner of the Nobel Prize in Physics, Frank Wilczek, and refers to a brand of detergent: the existence of the particles was supposed to 'clean up' the theory of physics, so to speak
Jörg Pretz, Sudy co-author and deputy director at Forschungszentrum Jülich's Nuclear Physics Institute and professor at RWTH Aachen University
Detecting these particles requires specialized methods, as they do not interact with the electromagnetic force and, thus, cannot be observed through conventional means.
How Do We Know Dark Matter Exists?
While dark matter is invisible, astronomers have long hypothesized its existence to explain anomalous gravitational effects observed in the universe.
The motions and velocities of stars in galaxies indicate the presence of unseen mass. For example, stars at the edges of spiral galaxies orbit at the same speeds as stars closer to the center, suggesting the presence of additional mass not visible to us.
"This was the only way to reconcile the velocity distribution of visible matter within galaxies with existing knowledge. A 'dark' form of matter, previously unobserved, must additionally stabilize the galaxies" stated Jörg Pretz.
The discovery of new galaxies like Dragonfly 44, composed mostly of dark matter, and the observation of galaxies lacking dark matter further support the idea.
According to Einstein, gravity governs the motion of stars and influences the path of light. Massive objects like galaxy clusters bend and distort the trajectory of light rays near them through gravitational lensing, enabling astronomers to map dark matter in the universe.
Several astronomical measurements have corroborated the existence of dark matter, leading to a worldwide effort to observe directly dark matter particle interactions with ordinary matter in extremely sensitive detectors, which would confirm its existence and shed light on its properties. However, these interactions are so feeble that they have escaped direct detection up to this point, forcing scientists to build detectors that are more and more sensitive.
The Gran Sasso National Laboratory in Italy (LNGS).
Despite numerous efforts, direct detection of dark matter particles with extremely sensitive detectors remains elusive, but ongoing research aims to shed more light on its properties.
JEDI's Novel Approach: Probing Dark Matter with Spin Polarization in Jülich particle accelerator COSY
The JEDI Collaboration has developed a novel experimental method to search for dark matter, axions, and axion-like particles (ALPs) using the quantum mechanical property of spin, which causes particles to behave like tiny bar magnets. The results are published in Physical Review X.
This search strategy assumes that ALPs may cause small vibrations in the spin of nucleons or light nuclei, corresponding to their mass frequency. If these vibrations exist, they could manifest as a coherent vibrational pattern lasting several seconds and covering a larger volume of space, making it feasible to measure these vibrations by examining the properties of the particle beam itself.
The researchers employed the particle accelerator Cooler Synchrotron (COSY) in Jülich, Germany, to circulate a polarized beam of deuterons with aligned nuclear spins. These spins would undergo precession due to magnetic fields maintaining the beam's orbit.
When the precession frequency aligns with the frequency of ALPs waves, a resonance will occur, rotating the polarization out of the ring plane and causing a vertical polarization change.
By constantly changing the spin precession frequency of the particle beam at COSY, researchers look for a polarization change, indicating a resonance that occurs when the precession frequency matches the frequency of ALP waves. This polarization change would signify the crossing of the resonance, potentially enabling the detection of dark matter particles if they interact with the beam.
Promising Beginnings: First Steps Toward Unraveling the Dark Matter Mystery
This study represents the first step in the search for dark matter, as no ALPs were detected. Nonetheless, the research narrowed down the potential interaction effect and provided valuable insights by establishing upper limits on coupling strengths between ALPs and deuterons, which will guide future investigations.
Theoretically, the background field of axions surrounding us could influence the behavior of spins, making it possible to detect their effects in the JEDI team's experiment. However, this effect is considered extremely small and beyond measurement accuracy.
Looking ahead, the JEDI team plans to search for axion-like particles in lighter mass ranges where other methods face challenges. Collaborating with a static electric dipole search in development and sharing access to the storage ring, which uses nearly identical technology, could prove beneficial. This joint effort will span many months, aiming to cover a significant range of frequencies with improved sensitivity.
Though this initial result lacked direct detection, the proposed method opened up a powerful new experimental avenue for unraveling the mysteries of dark matter. By continuously refining and enhancing the sensitivity of their searches, the JEDI team and their collaborators hope to unlock new insights into the elusive nature of dark matter and contribute to the broader understanding of the universe's mysterious constituents.
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References and Further Reading
CERN. (2023). Dark matter. [Online]. Available at: https://home.cern/science/physics/dark-matter
Jülich News. (2023). Search for Dark Matter at Jülich. [Online] Forschungszentrum Jülich. Available at: https://www.fz-juelich.de/en/news/archive/press-release/2023/search-for-dark-matter-at-julich
Karanth, S., Stephenson, E. J., Chang, S. P., Hejny, V., Park, S., Pretz, J., ... & Wüstner, P. (2022). First Search for Axion-Like Particles in a Storage Ring Using a Polarized Deuteron Beam. arXiv preprint arXiv:2208.07293. https://doi.org/10.1103/PhysRevX.13.031004
Bertone, G., & Hooper, D. (2018). History of dark matter. Reviews of Modern Physics, 90(4), 045002. https://doi.org/10.1103/RevModPhys.90.045002
Laboratori Nazionali del Gran Sasso. (2017). XENON1T, the most sensitive detector on Earth searching for WIMP dark matter, releases its first result. Available at: https://www.interactions.org/press-release/xenon1t-most-sensitive-detector-earth-searching-wimp-dark