Ann Arbor Times

One of the greatest puzzles in the universe is figuring out the nature of dark matter, the invisible substance that makes up most of the mass in our universe. New results from the world’s most sensitive dark matter detector, LUX-ZEPLIN (LZ), have narrowed down possibilities for one of the leading dark matter candidates: weakly interacting massive particles, or WIMPs.

LUX-ZEPLIN, abbreviated LZ, is a collaboration of 38 institutions, including the University of Michigan. Led by the Department of Energy’s Lawrence Berkeley National Laboratory, LZ hunts for dark matter from a cavern nearly one mile underground at the Sanford Underground Research Facility in South Dakota. The experiment’s new results explore weaker dark matter interactions than ever searched before and further limit what WIMPs could be.

“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 the detector and analysis techniques are performing even better than expected. “If WIMPs had been within the region we searched, we’d have been able to robustly say something about them,” he said. “We know we have the sensitivity and tools to see whether they’re there as we search lower energies and accrue the bulk of this experiment’s lifetime.”

The collaboration found no evidence of WIMPs above a mass of 9 gigaelectronvolts/c2 (GeV/c2). For comparison, the mass of a single proton is slightly less than 1 GeV/c2. The experiment’s sensitivity to faint interactions helps researchers reject potential WIMP dark matter models that don’t fit the data, leaving significantly fewer places for WIMPs to hide.

“We’ve demonstrated that LZ is very much a discovery-capable machine,” said LZ physics coordinator Scott Haselschwardt, a recent Chamberlain Fellow at Berkeley Lab and now an assistant professor at U-M. “If dark matter presents itself in this range, we’ll be ready to see it.”

Even though no dark matter signal was discovered in its latest batch of data, there will be more opportunities over LZ’s lifetime. “This result is only after 25% of our data, so we definitely need to get the other 75%,” said Gregory Rischbieter, a research fellow in U-M's Department of Physics and LZ calibration analysis coordinator who helped develop and fine-tune software modeling frameworks used for distinguishing dark matter signals from background noise.

“Although a signal is still eluding us, we have the world’s best detector for this range of dark matter. If anything, it’s more motivation to keep looking.” Wolfgang Lorenzon, professor of physics at U-M who helped join U-M with LZ collaboration in 2015 added: “It’s detective work... That we haven’t seen dark matter yet isn’t because of the instrument; it’s because dark matter hasn’t revealed itself yet.”

Kaiyuan “Sky” Shi, a graduate student in physics at U-M is also part of current U-M LZ cohort.

The new LZ results were presented at two physics conferences on Aug. 26: LIDINE 2024 in São Paulo and TeV Particle Astrophysics 2024 in Chicago where Haselschwardt delivered a presentation. A science paper will be published soon.

The results analyze 280 days’ worth data: new set collected between March 2023-April 2024 combined with earlier days from first run. Experiment plans collect total worth before ends in 2028.

“If you think search like buried treasure dug almost five times deeper anyone else past,” said Scott Kravitz deputy physics coordinator professor University Texas.“That something do million shovels—you inventing tool.”

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“We’re pushing boundary regime people not looked before,” said Haselschwardt.“There human tendency want see patterns really important enter bias wanders make discovery right.”Dark named emit reflect absorb light estimated make up mass never directly detected.Still left fingerprints multiple astronomical observations.Life wouldn’t exist without mysterious fundamental piece universe.Dark contributes gravitational attraction helps galaxies form stay together.Liquid xenon dense transparent material particles potentially bump nucleus causing move hit cue ball game pool collecting light electrons emitted captures alongside other data.“We’ve demonstrated strong search machine keep running getting better—but lots other things can do detector,” said Amy Cottle lead effort assistant professor next stage using look interesting rare processes rare decays atoms neutrinoless double beta decay boron-8 neutrinos sun beyond-the-Standard-Model addition probing interesting previously inaccessible models last years.”Collaboration roughly scientists institutions United States United Kingdom Portugal Switzerland South Korea Australia much work building operating analyzing record-setting done early career researchers.Collaboration already looking forward analyzing next set using tricks lower-mass thinking through potential upgrades improve planning next-generation called XLZD.“Our ability improving rate faster Moore Law curve everything nothing wait until comes next.”Supported Office Science High Energy Physics National Energy Research Scientific Computing Center DOE user facility supported Science & Technology Facilities Council Portuguese Foundation Swiss National Institute Basic acknowledges assistance Sanford Underground Research Facility.