What it is
Dark matter makes up roughly 85% of the mass in the Universe, but its particle nature is unknown. Among the leading candidates are weakly interacting massive particles, and the LUX-ZEPLIN (LZ) experiment, a xenon detector deep underground, recently reported a single nuclear-recoil 'event of interest' at 248 keV that it could not attribute to any known background, in tension with a background-only hypothesis at a global significance of 2.6 sigma (local 3.4 sigma). This paper proposes the event could be a Higgsino, the supersymmetric partner of the Higgs boson. A nearly pure Higgsino is a form of inelastic dark matter: two nearly identical neutral states, separated by a small mass splitting, scatter off a nucleus by converting one into the other. Because the same electroweak interaction that sets this coupling also fixes the scattering rate, the model is unusually predictive, with the mass splitting as the main free choice. The authors show that for a Higgsino mass near 1 TeV and a splitting near 350 keV, the predicted cross section approaches the two-sided 90% confidence interval LZ reported for the event.
Why it matters
A leading dark matter detector has an unexplained recoil event, and this work shows a well-motivated particle could produce it with no free interaction strength to tune. The Higgsino arises naturally in supersymmetric extensions of the Standard Model and, at a mass near 1 TeV, is thermally produced in the early Universe in roughly the right amount to be the dark matter. Testing the interpretation does not require new assumptions: because the splitting near 350 keV sits close to the largest value a xenon nucleus can probe, a dedicated LZ analysis and further exposure would show whether the signal strengthens or fades.
Underlined numbers link to their source. Every metric and quoted figure is listed under Sources and data below.
Filed underDark Matter and Cosmic Phenomena, Particle physics theoretical and experimental studies, Neutrino Physics Research
