Testing Dark Matter Coscattering with the High-Energy LZ Recoil

@misc{chakraborti2026testing,
  title = {{Testing Dark Matter Coscattering with the High-Energy LZ Recoil}},
  author = {Sreemanti Chakraborti and Soumyajit Datta},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.08648},
  eprint = {2610.08648},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.08648},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Testing Dark Matter Coscattering with the High-Energy LZ Recoil
AU  - Sreemanti Chakraborti
AU  - Soumyajit Datta
PY  - 2026
DA  - 2026/10/06
PB  - arXiv
DO  - 10.48550/arxiv.2610.08648
UR  - https://arxiv.org/abs/2610.08648
AB  - We investigate whether the high-energy nuclear recoil recently reported by LZ can probe dark matter (DM) whose relic abundance is set by coscattering, or conversion-driven freeze-out. We consider a singlet-doublet fermion DM model coupled to a light dark photon, in which the predominantly singlet-like DM state is separated from a more strongly interacting doublet-like state by a ∼ 100 keV mass splitting. In the small mixing regime, conversion into the doublet sector becomes the bottleneck controlling the relic abundance, realising coscattering, while the same small mixing would ordinarily suppress direct detection. A light dark photon enhances the endothermic transition χ_1 N→χ_2 N, allowing the conversion-driven region to be probed by high-energy nuclear recoils. We find that for m_A'=250 MeV the LZ-sensitive region can cover essentially the full relic-compatible parameter space, including the dominantly conversion-driven regime. As the mediator mass is increased, the LZ sensitivity progressively shifts towards larger singlet-doublet mixing, reducing its overlap with the coscattering region. Combining the relic density and recoil requirements selects DM masses extending approximately from 750 GeV to 1.6 TeV for the mediator masses considered. The LZ recoil can therefore directly test the same interaction and physical parameters that dominantly set the DM relic abundance, providing a probe of the same conversion mechanism across vastly different cosmological epochs.
ER  -