Suffolk Reporter

New results from the LUX-ZEPLIN (LZ) experiment, the world's most sensitive dark matter detector, have further constrained possibilities for weakly interacting massive particles (WIMPs), a leading dark matter candidate. The experiment, led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), operates nearly one mile underground at the Sanford Underground Research Facility in South Dakota.

“These are new world-leading constraints by a sizable margin on dark matter and WIMPs,” said Chamkaur Ghag, spokesperson for LZ and a professor at University College London (UCL). He noted that both the detector and analysis techniques are performing better than expected. “If WIMPs had been within the region we searched, we’d have been able to robustly say something about them.”

The collaboration found no evidence of WIMPs above a mass of 9 gigaelectronvolts/c2 (GeV/c2). This sensitivity helps researchers reject potential WIMP models that don't fit the data. The new results were presented at two physics conferences on August 26: TeV Particle Astrophysics 2024 in Chicago, Illinois, and LIDINE 2024 in São Paulo, Brazil. A science paper will be published soon.

The results analyze 280 days’ worth of data: 220 days collected between March 2023 and April 2024 combined with an earlier set of 60 days from LZ’s first run. The experiment plans to collect data until it ends in 2028.

“If you think of the search for dark matter like looking for buried treasure, we’ve dug almost five times deeper than anyone else has in the past,” said Scott Kravitz, LZ’s deputy physics coordinator and a professor at the University of Texas at Austin.

LZ’s sensitivity comes from its ability to reduce backgrounds or false signals that can mimic dark matter interactions. Deep underground, it is shielded from cosmic rays. Built from ultraclean parts to reduce natural radiation and using sophisticated analysis techniques to rule out background interactions such as radon, LZ ensures precise detection capabilities.

This result marks the first time LZ has applied “salting”– adding fake WIMP signals during data collection to avoid unconscious bias until final analysis.

“We’re pushing the boundary into a regime where people have not looked for dark matter before,” said Scott Haselschwardt, LZ physics coordinator and assistant professor at the University of Michigan.

Dark matter constitutes approximately 85% of the universe's mass but has never been directly detected. It does not emit or absorb light but influences gravitational attraction essential for galaxy formation.

LZ uses liquid xenon as its detection medium. When a WIMP collides with a xenon nucleus, it emits light and electrons captured by LZ detectors.

“We’ve demonstrated how strong we are as a WIMP search machine,” said Amy Cottle, lead on the WIMP search effort and assistant professor at UCL. She added that future stages would explore other rare physics processes alongside continuing dark matter searches.

The collaboration involves roughly 250 scientists from institutions across six countries: United States, United Kingdom, Portugal, Switzerland, South Korea, and Australia. Early career researchers play significant roles in building and analyzing this record-setting experiment.

“Our ability to search for dark matter is improving at a rate faster than Moore’s Law,” Kravitz stated. Plans include further improvements to LZ and developing next-generation detectors like XLZD.

LZ receives support from multiple entities including U.S., UK government agencies; Portuguese Foundation for Science; Swiss National Science Foundation; Institute for Basic Science Korea; along with over thirty-eight higher education institutions globally.

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