The LUX-ZEPLIN (LZ) experiment will be the world’s most sensitive dark matter detector. More recently, it has scored quite a spectacular success in whittling down the list of the leading contenders for dark matter, known as weakly interacting massive particles (WIMPs). Collectively, nearly 250 scientists are collaborating on this large-team effort. Their deeply collaborative nature aside, they originated from just 38 institutions, spanning the United States, United Kingdom, Portugal, Switzerland, South Korea, and Australia.
Constructed deep underground to minimize background noise, LZ’s 2,000-pound detector is housed almost a mile underground in the Sanford Underground Research Facility (SURF) in South Dakota. It is specially engineered to reduce the effects of natural radiation. As of writing, the experiment has successfully collected 280 days of data. This includes a new slate of 220 days gathered from March 2023 to April 2024, plus an extra 60 days from its original run. The partnership’s goal is to gather 1,000 days of behavioral data before the collaboration ends in 2028.
Unraveling the Mysteries of Dark Matter
Dark matter is one of the most confounding concepts in contemporary physics. The scientific community agrees that it makes up around 27% of the universe, but what that is escapes detection. In theory, WIMPs are one of the best dark matter candidates out there. The LZ collaboration has developed an extremely sophisticated system in order to detect interactions that could only come from WIMPs.
The LZ detector consists of two nested, actively-cooled titanium pressure vessels filled with ten tons of transparent pure liquid xenon. This unique configuration enables measurements thousands of times more sensitive than state-of-the-art, dramatically reducing background noise from other sources. Surrounding this core is the Outer Detector (OD), built from plastic tanks filled with gadolinium-loaded liquid scintillator. This combination is especially important for separating true dark matter signals from background noise that may mimic these interactions.
“Deep underground, the detector is shielded from cosmic rays coming from space.”
The detector’s design greatly increases its sensitivity, using different techniques to minimize background noise. LZ uses UV light to scan for dust contamination within the time-projection chamber. This iteration helps to avoid the accidental smothering of any promising signals.
The Role of Advanced Techniques
To increase the rigor and validity of its results and remove unintentional bias, LZ uses a method known as “salting.” This approach injects simulated WIMP signals into the data stream as the data are being collected. This means that if signals are detected, they can be accurately decoded. The experiment’s innovative design allows it to address rare events in physics, leading to broader implications beyond dark matter searches.
“Our experiment is also sensitive to rare events with roots in diverse areas of physics,” – Amarasinghe
In his closing comments, Amarasinghe highlighted the significance of these findings. He pointed out how dark matter searches could open a window to understanding other rare processes, such as solar neutrinos and specific xenon isotopes decaying. The enthusiasm inspired by these findings helps to support the continuation of research and discovery in the field.
Collaboration and Future Directions
The LZ collaboration is a prime example of what’s possible when scientists come together to advance discovery. The project demonstrates an impressive dedication to promoting dark matter research. It has been built out of the collective contributions of a number of institutions around the world—with strong contributions from UCSB.
“The UCSB Physics Department has a long history of devising searches for dark matter, starting with one of the first published results of a search in 1988,” – Nelson
Business researchers understand the many perils that await their journey. But as they venture into deeper, trickier territory, they have a much greater chance of being misunderstood. This is a result of our human instinct to look for patterns in data.
“There’s a human tendency to want to see patterns in data, so it’s really important when you enter this new regime that no bias wanders in. If you make a discovery, you want to get it right,” – Haselschwardt
Challenges such as neutron interactions further complicate the detection process, since neutrons can produce signals that are very similar to those produced by WIMPs. The Outer Detector tows the line in this delicate dance. It verifies or rules out possible WIMP detections by measuring the activity of neutrons.
“The tricky thing about neutrons is that they also interact with the xenon nuclei, giving off a signal identical to what we expect from WIMPs,” – Trask
Even with these challenges, researchers are hopeful – both about what they’ve found and what’s still possible to discover.
Looking Ahead
The LZ experiment, the world’s most sensitive dark matter detector, is currently collecting data. Scientists remain committed to improving their methods while expanding their knowledge about dark matter. The findings announced so far have been crucial to placing limits on what dark matter can and cannot be.
“While we always hope to discover a [new particle], it is important for particle physics that we are able to set bounds on what the [dark matter] might actually be,” – Hugh Lippincott
The historic work at LZ goes below the surface to burnish our knowledge of dark matter. It opens doors to many other exciting areas within physics. Backed by a collaborative team and innovative technology, the LZ collaboration is ready to usher in an exciting new era of discoveries in the field.