Dark Matter Detector Releases Best-Yet Result
From one mile underground in a disused South Dakota gold mine, the LUX-ZEPLIN (LZ) experiment has been hunting for dark matter since 2021. Physicists expect that some of the signals emanating from its liquid-xenon-filled chamber come from weakly interacting massive particles (WIMPs), a leading dark matter candidate. Now the LZ Collaboration reports that a search through 280 days of data uncovered no evidence of WIMPs above a mass of 9 GeV/c2 [1]. The search imposes constraints on WIMP parameters that are nearly 5 times more stringent than the previous best.
Xenon was chosen as the detector material in the LZ experiment because xenon nuclei have a high atomic mass and xenon liquid has a high density. Both properties boost the chance that a WIMP will interact with a xenon proton or neutron. What’s more, the liquid is transparent to the photons and electrons produced by such interactions, so these particles are readily detectable. By tracking differences in the timing and magnitude of the signals from the two particle types, the LZ experiment can pick out WIMPs from background events, which arise primarily from trace radioactive isotopes in and around the detector.
The LZ Collaboration’s latest analysis used new and improved background discrimination to identify a total of 1220 events. Using models of how WIMPs of various masses should interact with the chamber’s 7 metric tons of liquid xenon, the researchers drew two main conclusions. First, none of the detected events were caused by WIMPs with mass over 9 GeV/c2. Second, the cross section for a 40-GeV/c2 WIMP striking a xenon proton or neutron has a minuscule upper bound of 2.2 × 10–48 cm2. These new limits narrow the range of viable theories.
–Rachel Berkowitz
Rachel Berkowitz is a Corresponding Editor for Physics Magazine based in Vancouver, Canada.
References
- J. Aalbers et al., “Dark matter search results from 4.2 tonne-years of exposure of the LUX-ZEPLIN (LZ) experiment,” Phys. Rev. Lett. 135, 011802 (2025).