A Narrow Neutrino Window for the LZ Event
Abstract
The LUX-ZEPLIN (LZ) experiment has reported an event consistent with a $248$ keV nuclear recoil. Explaining the absence of lower-energy recoil events typically calls for some form of upscattering that kinematically forbids such events. In this work, we present a framework in which the LZ observation has a neutrino origin, with atmospheric neutrinos providing the dominant flux in the required energy range. A scenario in which atmospheric neutrinos upscatter to a heavier neutral state would also produce a large number of neutral-current events in neutrino experiments. In particular, scattering on lighter nuclear targets results in much larger nuclear recoil energies compared to xenon, yet no such excess has been observed. We show that this constraint from neutrino experiments can be evaded if atmospheric neutrinos within a narrow energy window first produce a nearly monoenergetic state N1, followed by the upscattering of N1 to its heavier partner N2 in LZ. In such a scenario, scattering on xenon becomes kinematically allowed for N2 masses around $250$ MeV, while scattering on oxygen, carbon, and other targets used in large-scale neutrino experiments remains kinematically forbidden. We show that this two-step process, ν→ N1 → N2, can be realized through a parametric resonance induced by a dark matter background that efficiently produces N1, followed by N1 → N2 upscattering mediated by a vector boson in a model with gauged U(1)B. The latter interaction can be sufficiently stronger than the weak interaction, which is necessary to lift the neutrino floor and yield 𝒪(1) event at LZ.
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BibTeX
@misc{brdar2026narrow,
title = {{A Narrow Neutrino Window for the LZ Event}},
author = {Vedran Brdar and Dibya S. Chattopadhyay},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.30255},
eprint = {2609.30255},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.30255},
}
RIS
TY - UNPB
TI - A Narrow Neutrino Window for the LZ Event
AU - Vedran Brdar
AU - Dibya S. Chattopadhyay
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.30255
UR - https://arxiv.org/abs/2609.30255
AB - The LUX-ZEPLIN (LZ) experiment has reported an event consistent with a $248$ keV nuclear recoil. Explaining the absence of lower-energy recoil events typically calls for some form of upscattering that kinematically forbids such events. In this work, we present a framework in which the LZ observation has a neutrino origin, with atmospheric neutrinos providing the dominant flux in the required energy range. A scenario in which atmospheric neutrinos upscatter to a heavier neutral state would also produce a large number of neutral-current events in neutrino experiments. In particular, scattering on lighter nuclear targets results in much larger nuclear recoil energies compared to xenon, yet no such excess has been observed. We show that this constraint from neutrino experiments can be evaded if atmospheric neutrinos within a narrow energy window first produce a nearly monoenergetic state N_1, followed by the upscattering of N_1 to its heavier partner N_2 in LZ. In such a scenario, scattering on xenon becomes kinematically allowed for N_2 masses around $250$ MeV, while scattering on oxygen, carbon, and other targets used in large-scale neutrino experiments remains kinematically forbidden. We show that this two-step process, ν→ N_1 → N_2, can be realized through a parametric resonance induced by a dark matter background that efficiently produces N_1, followed by N_1 → N_2 upscattering mediated by a vector boson in a model with gauged U(1)_B. The latter interaction can be sufficiently stronger than the weak interaction, which is necessary to lift the neutrino floor and yield 𝒪(1) event at LZ.
ER -