The LUX-ZEPLIN (LZ) experiment recently reported an anomalous event consistent with a nuclear recoil of approximately 248 keV. Such high-energy recoil events are of significant interest for dark matter (DM) searches. A new study has investigated the inelastic xenon channel (χ + Xe → χ + Xe*), which offers a complementary pathway to interpret these recoils, especially if caused by dark matter particle interactions. This channel involves the excitation of the xenon nucleus after interaction, rather than just an elastic recoil.

The researchers utilized the non-relativistic effective-field-theory (NREFT) framework and nuclear shell models to compute inelastic interaction rates. They simulated the detector's S1-S2 responses, validating their model against public LZ data. The nuclear de-excitation resulting from an inelastic interaction adds an electromagnetic component to the signal, shifting it towards the electronic recoil band and, in some cases, towards backgrounds from isotopes. To address this, they developed a schematic background model and performed a simplified statistical analysis.

Results indicate that, for most dark matter scenarios studied, the inelastic xenon interaction rate is approximately an order of magnitude lower (around 0.1) than the elastic rate. This suggests that significantly larger exposures are required in future experiments for this complementary channel to become conclusively observable. The study highlights the importance of isotope-induced background structures in the extended-energy region and broadens the phenomenology of inelastic xenon signatures to a wider range of dark matter models, which will be crucial for future DM searches.