Xenon Isotope Filtering at the Kinematic Edge of Inelastic Dark Matter
Abstract
Motivated by high-energy xenon recoil searches, we study isotope-dependent endothermic dark-matter scattering near the upper speed boundary of a truncated Galactic halo. Small differences among xenon nuclear masses shift the minimum incident speed and can be strongly amplified when the required velocity approaches the end of the halo distribution. We formulate the isotope-resolved coherent-contact rate and separate this kinematic filtering from high-momentum nuclear suppression. For mχ=1.1 TeV, δ=365 keV, and ER=248 keV, the kinematic-only benchmark gives f136kin≃0.289, while after Helm weighting the largest contribution is f132≃0.346 and the 136Xe fraction falls to ≃0.094. For idealized pure-isotope targets at fixed detector mass, microscopic coupling, and halo, the integrated $225−−271~\keV$ responses relative to natural xenon are approximately $0.404$, $1.235$, and $1.693$ for 129Xe, 132Xe, and 136Xe, respectively. A single effective-xenon nucleus also fails to reproduce the full isotope sum accurately near the edge, changing the benchmark window rate by about 8% and producing larger spectral distortions. These quantitative results depend on the high-speed halo and on the assumed nuclear response; the isotope-dependent kinematic support does not. The calculation is a theory-level diagnostic rather than an LZ likelihood fit or event-by-event isotope identification.
Related
- Implications of Inelastic Dark Matter for Primordial Dark-Star Evolution: Kinematic Thresholds and Nonthermal Capture
- For Whom the Xenon Recoils: Magnetic Inelastic Dark Baryons
- Inelastic from the Other Side: Xenon Excitation Signals in Light of the LZ High-Recoil Event
- MOTION, a liquid xenon time projection chamber platform for high voltage technologies in dark matter detectors
- Direct detection constraints on EFT operators for inelastic dark matter
BibTeX
@misc{ahmed2026xenon,
title = {{Xenon Isotope Filtering at the Kinematic Edge of Inelastic Dark Matter}},
author = {Waqas Ahmed and Ammara Ahmad and Mansoor Ur Rehman},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.15634},
eprint = {2609.15634},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.15634},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Xenon Isotope Filtering at the Kinematic Edge of Inelastic Dark Matter
AU - Waqas Ahmed
AU - Ammara Ahmad
AU - Mansoor Ur Rehman
PY - 2026
DA - 2026/09/14
PB - arXiv
DO - 10.48550/arxiv.2609.15634
UR - https://arxiv.org/abs/2609.15634
AB - Motivated by high-energy xenon recoil searches, we study isotope-dependent endothermic dark-matter scattering near the upper speed boundary of a truncated Galactic halo. Small differences among xenon nuclear masses shift the minimum incident speed and can be strongly amplified when the required velocity approaches the end of the halo distribution. We formulate the isotope-resolved coherent-contact rate and separate this kinematic filtering from high-momentum nuclear suppression. For m_χ=1.1 TeV, δ=365 keV, and E_R=248 keV, the kinematic-only benchmark gives f_136^kin≃0.289, while after Helm weighting the largest contribution is f_132≃0.346 and the ^136Xe fraction falls to ≃0.094. For idealized pure-isotope targets at fixed detector mass, microscopic coupling, and halo, the integrated $225−−271~\keV$ responses relative to natural xenon are approximately $0.404$, $1.235$, and $1.693$ for ^129Xe, ^132Xe, and ^136Xe, respectively. A single effective-xenon nucleus also fails to reproduce the full isotope sum accurately near the edge, changing the benchmark window rate by about 8% and producing larger spectral distortions. These quantitative results depend on the high-speed halo and on the assumed nuclear response; the isotope-dependent kinematic support does not. The calculation is a theory-level diagnostic rather than an LZ likelihood fit or event-by-event isotope identification.
ER -