Cosmic ray electron boosted light dark matter: Implications of LZ 2025 data

Abstract

Current multi-ton detectors put stringent constraints on the GeV-scale galactic dark matter, pushing the allowed cross-section almost towards the neutrino fog, yet remain mostly insensitive to the light dark matter. Cosmic rays can upscatter the non-relativistic halo dark matter particles, making a sub-population of them gain sufficient kinetic energy to be discernible in current direct search experiments. In this work, we explore this alternate strategy to probe sub-MeV electrophilic dark matter boosted by cosmic rays with the latest data of LZ 2025 (WS2024 run) and improve the constraint on the MeV scale dark matter by almost $\sim\mathcal{O}(1)$ compared to the previous XENONnT limit for energy-independent cross-section. Using realistic energy-dependent cross-sections, we also analyse such a scenario, where the associated mediator mass plays a crucial role in governing the event rate and hence the expected limits too. With energy-dependent cross-sections, our obtained limits also remain stronger than the existing constraints from current direct detection experiments. Even compared to the limits from the neutrino detectors with a larger target size, LZ 2025 can put stringent constraints in certain parameter space of the mediator, excluding the previously unexplored regions.

Figures (6)

• Figure 1: $2\sigma$ C.L. constraints on CRe boosted DM with constant cross-section from LZ 2025 is shown by purple shaded region. Existing constraints from BDM search at XENONnT Guha:2024mjr (dashed blue line), solar reflected DM An:2017ojc (orange shaded region) and the combined DD limits from SuperCDMS SuperCDMS:2018mne, SENSEI Crisler:2018gci, and XENON10 Essig:2012yx for galactic halo DM (grey shaded region) are also shown.
• Figure 2: $2\sigma$ C.L. constraints on CRe boosted DM in the heavy mediator limit ($F_{\rm DM}(q)=1$) with (a) vector mediator and (b) scalar mediator from LZ 2025 are shown by purple shaded region. Existing constraints from BDM search at XENONnT Guha:2024mjr (dashed blue line) and the combined DD limits from SuperCDMS SuperCDMS:2018mne, SENSEI Crisler:2018gci, and XENON10 Essig:2012yx for galactic halo DM (grey shaded region) are also portrayed.
• Figure 3: $2\sigma$ C.L. constraints on CRe boosted DM in the light mediator limit ($F_{\rm DM}(q)=(\alpha m_e)^2/q^2$) with (a) vector mediator and (b) scalar mediator from LZ 2025 are shown by purple shaded region. Existing constraints from BDM search at XENONnT Guha:2024mjr (dashed blue line) and DAMIC 2025 DAMIC-M:2025luv limit for galactic halo DM (grey shaded region) are also portrayed.
• Figure 4: $2\sigma$ C.L. constraints in the vector mediator mass vs. coupling parameter space for CRe boosted DM from LZ 2025. Limits corresponding to $m_\chi=1$ MeV, 10 MeV and $100$ MeV are represented by the region above the purple, orange and blue solid lines respectively.
• Figure 5: Expected recoil signature of CRe boosted DM in LZ detector LZ:2025zpw for (a) heavy mediator with $m_\chi=1$ MeV and (b) light mediator with $m_\chi=0.1$ MeV.