Nuclear Recoils from Invisible Neutron-Pair Annihilation and the LZ event
Abstract
Two bound neutrons can annihilate into a single invisible scalar carrying baryon number two, producing a monochromatic nuclear recoil. Pair removal connects the 0+ ground states of even-even nuclei and, for several detector isotopes, leaves a stable daughter where single-neutron removal would leave a radioactive one. Below the first daughter excitation, the leading transition produces neither nuclear de-excitation nor subsequent daughter decay. We identify the corresponding mass windows in argon and xenon, including argon recoils up to 108 keV, and obtain an approximate partial-lifetime bound of 8.5 × 1026 yr from DEAP-3600 data. We also discuss this mechanism as a possible origin of the 248 keV recoil candidate reported by LZ. A ground-state interpretation points to a scalar mass near 1.85 GeV, where daughter excitations are also accessible, and motivates searches for correlated higher-energy recoil lines in argon. Recoil lines in different isotopes reconstruct a common invisible-particle mass. The emitted scalar can itself be dark matter, making these searches a probe of ordinary matter converting into a dark sector.
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BibTeX
@misc{lee2026nuclear,
title = {{Nuclear Recoils from Invisible Neutron-Pair Annihilation and the LZ event}},
author = {Junseok Lee and Fuminobu Takahashi and Yu-Dai Tsai},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.12045},
eprint = {2609.12045},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.12045},
}
RIS
TY - UNPB
TI - Nuclear Recoils from Invisible Neutron-Pair Annihilation and the LZ event
AU - Junseok Lee
AU - Fuminobu Takahashi
AU - Yu-Dai Tsai
PY - 2026
DA - 2026/09/29
PB - arXiv
DO - 10.48550/arxiv.2609.12045
UR - https://arxiv.org/abs/2609.12045
AB - Two bound neutrons can annihilate into a single invisible scalar carrying baryon number two, producing a monochromatic nuclear recoil. Pair removal connects the 0^+ ground states of even-even nuclei and, for several detector isotopes, leaves a stable daughter where single-neutron removal would leave a radioactive one. Below the first daughter excitation, the leading transition produces neither nuclear de-excitation nor subsequent daughter decay. We identify the corresponding mass windows in argon and xenon, including argon recoils up to 108 keV, and obtain an approximate partial-lifetime bound of 8.5 × 10^26 yr from DEAP-3600 data. We also discuss this mechanism as a possible origin of the 248 keV recoil candidate reported by LZ. A ground-state interpretation points to a scalar mass near 1.85 GeV, where daughter excitations are also accessible, and motivates searches for correlated higher-energy recoil lines in argon. Recoil lines in different isotopes reconstruct a common invisible-particle mass. The emitted scalar can itself be dark matter, making these searches a probe of ordinary matter converting into a dark sector.
ER -