LZ Reports One Unexplained Event at 2.6 Sigma in High-Energy WIMP Search

LZ analyzed data collected from March 2023 to April 2024 using its 10-tonne liquid xenon target at SURF. Researchers expanded the search beyond the standard low-energy WIMP window to include higher-energy nuclear recoils, applying tighter fiducial cuts and improved background modeling that reduced expected backgrounds to well below one event in the signal region. One event survived all cuts, producing a 2.6-sigma excess.

This result aligns with earlier hints from XENONnT and PandaX-4T of possible high-mass WIMP signals but remains far below the 5-sigma threshold required for discovery. The event’s energy and timing are consistent with a spin-independent interaction cross-section roughly an order of magnitude below current limits, which would require either a heavier WIMP or a non-standard coupling if confirmed.

Future runs through 2027 are projected to accumulate more than 1,000 live days. If the rate is real, the collaboration expects two to four additional events; zero events would drop the significance below 1 sigma and effectively close this parameter space for the simplest WIMP models.