Located deep in the Black Hills of South Dakota, the world’s largest dark matter The detector has begun to search for this elusive and mysterious form of matter.
The LUX-ZEPLIN (LZ) experiment is specially adapted to detect a particular type of hypothetical dark matter particle, called Weakly Interacting Massive Particles, or WIMPs. The detector began operating for the first time in December 2021, and we already have its first results. the findings, posted on the LZ experiment websiteshow that it is the world’s most sensitive dark matter probe – sensitive enough, its operators hope, to directly detect dark matter for the first time. In the process, the 250 or so scientists operating LZ could solve one of the most pressing questions in science.
The dark matter puzzle is so important to physicists because the ordinary baryonic matter that comprises the everyday “stuff” we see around us, as well as all of the universe planets, stars, and gas clouds—represents only 5 percent of its matter and energy budget. The rest represents the so-called “dark universe” made up of mysterious dark energy and dark matter.
While dark energy, which drives the universe’s accelerating expansion, accounts for 70 percent of this budget, dark matter makes up the remaining 25 percent. This means that when energy is removed from the equation, dark matter it represents more than 80 percent of the content of the universe.
“We live in a special time, most of the universe is a mystery that we currently cannot explain. What is dark matter? What is dark energy?” Kevin Lesko, a senior physicist at Berkeley Lab and a former spokesman for LZ, says Folk Mechanics. “Physicists, cosmologists and astronomers are working very diligently right now to understand them better.”
What are WIMPs?
Detecting dark matter is so difficult despite its abundance because it doesn’t interact with electromagnetic radiation. This is what tells us that dark matter is not made up of atoms made up of protons and neutrons (baryons ), and is very different from ordinary matter.
The only way astronomers have been able to infer its presence is through its interaction with gravity. If it weren’t for the gravitational effects of dark matter, galaxies they’re spinning so fast they’d be blown to pieces. But there could be another way to detect dark matter. If it is made up of WIMPs, dark matter should interact very weakly with ordinary baryonic matter, also known as visible matter.
WIMPs are thought to be heavy, slow-moving particles with masses between one and 1,000 times that of a proton, created in the early universe like other subatomic particlescollided As the universe expanded and cooled, these collisions became increasingly rare. Dark matter theories suggest that this process left us with exactly enough WIMPs to account for the amount of dark matter we measure today, about five times more than ordinary matter.
WIMPs interact with baryonic matter through the weak nuclear force, one of the forces in the universe. four fundamental forces– and it’s so slight that it requires an immensely sensitive detector to detect it. That’s where the LZ experiment comes in.
What is the LUX-ZEPLIN experiment?
The LZ experiment contains a multi-level detection system and exists under precisely designed environmental conditions to remove as much “noise” from background sources as possible. Planning for the detector began nine years ago with manufacturing at the Sanford Laboratory in South Dakota beginning two years later.
At the heart of the LZ detector are two titanium tanks containing around ten tons of liquid. xenon. This xenon must be kept at -148 degrees Fahrenheit (-100 degrees Celsius); The scientists selected this element for the experiment because it can be made extremely dense and very pure. Since interaction between WIMPs and ordinary matter is proposed to be very rare, the more xenon the detector can use, the better the chance of detecting such an event. The xenon “target” of the LZ experiment is larger than that of any other dark matter detector.
The xenon cells are surrounded by an array of photomultiplier tubes (PMTs) containing 500 sensitive light detectors designed to detect faint flashes of light. “When the particles collide with xenon atoms, the atoms scintillate, giving off a tiny flash of light, and atomic electrons can be knocked off as the xenon ionizes.” Lesko explains. “Electrons are diverted [to] the upper part of the xenon by applying an electric field to it. When the electrons reach the top, they are pulled out of the liquid by a stronger electric field into a layer of gas above the liquid. Once there, the electrons produce a second flash of light.”
The time difference between these two flashes allows the researchers to determine the depth in the tanks at which the interaction occurred. “So we can determine the 3D position of each event,” says Lesko. “The two flashes of light give us information about the energy of the interaction and help us distinguish background events from possible WIMP events.”
Surrounding this setup is a water tank that helps protect the experiment from the bottom. radiation. “We checked the radioactivity of every component in the detector by analyzing every item, every nut, bolt, screw, wire, Teflon piece, and tin piece in the instrument, producing the most radio-pure dark matter detector ever.” lesko says. “The careful engineering, fabrication, and integration of the components, which came from all over the world, create a very well-tuned and effective instrument for searching for dark matter interactions and rejecting background radiation.”
Outside of this is a second, larger detection system. The purpose of this is to eliminate false positives by detecting particles that could create dark matter-like interactions, particularly neutrons. The LZ experiment is also shielded from high-energy charged particles from the sun and other cosmic sources, called cosmic rays, by its location nearly a mile underground.
The results so far
While the first results from the LZ experiment contain no hint of dark matter, Lesko points to several positive aspects of the initial research that was collected during the first three months of its operations.
“I have three important points to take away from this first analysis. First of all, our record is as low as we expected. Second, the detector works well and is able to search for dark matter effectively,” says Lesko. “Finally, it is working so well that with three months of data we have been able to establish a world-leading result, outperforming previous experiments, many of which ran for years.”
🤯 More mind-blowing physics
Over the next 1,000 days, the sensitivity of the LZ experiment will increase further, meaning its operators are right to be optimistic about its potential contribution to our understanding of the universe.
“We look forward to what we will find in the next few years,” Lesko concludes. “It is our hope that entirely new chapters will be written for our textbooks, media articles, and popular press in the near future.
“This is an exciting time for all of us.”
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