How the world’s most sensitive dark matter detector is changing our understanding of the universe
Since the 1880s, scientists have hypothesized that something was missing from the universe. The galaxies around us, with all the matter that we could observe, were rotating at such a high speed that scientists believed they should have been torn apart long ago (1). Thus, scientists thought that there was an invisible type of matter that made up about 85% of all mass in the universe and kept galaxies massive enough to stay together (1, 2). Today, this hypothesis has evolved into the “dark matter hypothesis,” with modern-day scientists believing that a large portion of the universe’s mass is made up of an invisible, unknown substance.
Scientists believe dark matter does not interact with electromagnetic forces, meaning that it neither emits, reflects, nor absorbs any light, which makes it virtually undetectable (1). One idea is that dark matter are “supersymmetric particles,” hypothetical matter particles that are “partners” of different types of matter already known to exist (1). However, most scientists currently believe that dark matter is made up of weakly interacting massive particles (WIMPS), which would interact with normal matter only rarely and with an extremely small amount of force (3). The LUX-ZEPLIN (LZ) dark matter experiment in Lead, South Dakota, is working to detect and prove the existence of WIMPS (4).
A diagram of the LUX-ZEPLIN detector.
Formed in 2012 through the combination of two previous dark matter detectors, LUX (Large Underground Xenon), and ZEPLIN (ZonEd Proportional scintillation in LIquid Noble gases), the LUX-ZEPLIN dark matter experiment operates 4,850 feet underground, shielded from outside disturbances, to detect traces of WIMPS (4). LZ works by searching for reactions and movement of xenon atoms within a tank of more than seven tons of liquid xenon, since xenon is a very sensitive element (4). If a WIMP collides with or interacts with an atom, it is expected to produce light that can be captured by LZ’s 494 main photomultiplier tubes–specialized sensors made to detect small quantities of light–positioned above and below the xenon tank (3, 4). LZ also has 251 additional photomultiplier tubes to capture any light that may have escaped from the tank’s sides, ensuring that any trace of WIMPs will be detected. This makes the apparatus more sensitive by a factor of 50 compared to previous detectors (4). In addition, since LZ uses electric fields in combination with liquid xenon to create a two-phase “Time Projection Chamber,” the 250 scientists operating LZ can determine the direction of travel of any detected particles (4). Auxiliary veto detectors surrounding the apparatus also make sure that there are no background signals to cause any false readings (4).
After analyzing 280 days of data, the scientists at LZ have not yet detected the existence of dark matter. However, they have managed to narrow down what a WIMP might look like, finding that no WIMPs exist above a mass of nine gigaelectronvolts/c^2, which is about nine times the mass of a proton (2, 3, 4, 5). The results of the LZ study are nearly five times more precise than the previous study’s results (2, 3, 5). Although dark matter remains undiscovered, the LZ experiment plans to collect 1,000 days of data before it ends in 2028, leaving opportunities for new breakthroughs (4, 5). The future of dark matter research and LUX-ZEPLIN is just starting, with limitless possibilities and unprecedented potential. As scientists continue to probe the mysteries of dark matter, experiments like LUX-ZEPLIN bring us closer to unlocking the secrets of the universe’s unseen foundation.
Bibliography:
- Dark matter. (2024, December 4). CERN. https://home.cern/science/physics/dark-matter
- Fell, A. (2024, August 26). LZ Experiment Sets New Record in Search for Dark Matter. UC Davis. https://www.ucdavis.edu/curiosity/news/lz-experiment-sets-new-record-search-dark-matter
- Advancing the quest for dark matter: New insights from the LUX-ZEPLIN experiment. (2025, January 8). Brown University. https://www.brown.edu/news/2024-08-26/dark-matter-lz
- The LZ Dark Matter Experiment | The status and science of the LZ dark matter experiment. (2020). Lbl.gov. https://lz.lbl.gov/
- SSUH. (2024, August 26). LZ Experiment Sets New Record in Search for Dark Matter. Berkeley Lab News Center. https://newscenter.lbl.gov/2024/08/26/lz-experiment-sets-new-record-in-search-for-dark-matter/
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