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

TL;DR

This paper investigates how cosmic ray-boosted light dark matter can be detected using the LZ 2025 experiment, providing improved constraints on sub-MeV dark matter and exploring the impact of mediator mass on detection prospects.

Contribution

It introduces a novel approach to detect sub-MeV dark matter via cosmic ray boosting and analyzes the effects of energy-dependent cross-sections and mediator mass on detection limits.

Findings

LZ 2025 data improves constraints on MeV dark matter by an order of magnitude.

Cosmic ray boosting enhances the detectability of light dark matter in direct detection experiments.

New parameter space regions are excluded, surpassing previous constraints from neutrino detectors.

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.