DM induced neutron disappearance as the origin of the LZ nuclear recoil event

Abstract

We investigate dark-matter-induced neutron disappearance as an interpretation of the high-energy nuclear recoil event reported by LUX-ZEPLIN. An incoming dark matter (DM) particle annihilates a bound neutron into an invisible scalar, leaving a recoiling daughter nucleus. For each accessible daughter state, two-body kinematics fixes the recoil energy in the zero-velocity limit, producing a line spectrum broadened by halo velocities. We identify parameter regions for benchmark DM masses of 5 and 50 GeV that can account for the event near 248 keV without producing events at lower energy. We examine collider constraints in an illustrative ultraviolet completion and recast Borexino data to constrain accompanying nuclear de-excitation signals. More generally, the DM-induced neutron disappearance provides a framework for interpreting localized nuclear recoil excesses in future direct-detection experiments.