One event in LZ revives hypotheses about dark matter

The LUX-ZEPLIN (LZ) experiment searches for dark matter particles using liquid xenon. In an exposure of 2.84 tonne-years, the collaboration recorded one event consistent with a xenon nucleus recoiling. It is a clue to investigate, not a confirmed detection of dark matter.

The analysis estimated a recoil energy of 248 kiloelectronvolts, with statistical and systematic uncertainties of 23 kiloelectronvolts each. Significance reached 3.4 sigma in the strongest local case and 2.6 sigma globally after accounting for the different models tested. Lower significance means greater compatibility with a background fluctuation.

A later hypothesis proposed a higgsino, a particle predicted by supersymmetry models and related to the Higgs boson. Katherine Freese and Dionysios Theodosopoulos explored this possibility in theoretical work. LZ reported the event and studied possible backgrounds; the collaboration did not claim to identify a higgsino.

Experiments such as LZ try to separate rare signals from ordinary interactions caused by natural radioactivity and other processes. Researchers examined alternative origins for the event, but one record cannot definitively distinguish new physics from a background that has not yet been modeled.

The data justify follow-up and further analysis, but they do not support a headline claiming dark matter has been discovered. The LZ Collaboration reported the result, with Sam Eriksen presenting the analysis; the higgsino proposal is an independent theoretical interpretation. More data and compatible events will be decisive.