# Constraints on Spin-Independent Nucleus Scattering with sub-GeV Weakly Interacting Massive Particle Dark Matter from the CDEX-1B Experiment at the China Jin-Ping Laboratory

## TL;DR

This paper reports new experimental limits on sub-GeV WIMP dark matter interactions using the CDEX-1B detector, incorporating the Migdal effect to extend sensitivity to lower masses and analyzing both time-integrated and annual modulation signals.

## Contribution

It introduces the first constraints on sub-GeV WIMPs with Migdal effect included, expanding the detectable mass range and improving limits on spin-independent cross sections.

## Key findings

- Set new upper limits on WIMP-nucleus cross sections for masses 50 MeV/c^2 to 3 GeV/c^2.
- Demonstrated the effectiveness of incorporating the Migdal effect in low-mass WIMP searches.
- Extended the sensitive mass window by an order of magnitude compared to previous results.

## Abstract

We report results on the searches of weakly interacting massive particles (WIMPs) with sub-GeV masses ($m_{\chi}$) via WIMP-nucleus spin-independent scattering with Migdal effect incorporated. Analysis on time-integrated (TI) and annual modulation (AM) effects on CDEX-1B data are performed, with 737.1 kg$\cdot$day exposure and 160 eVee threshold for TI analysis, and 1107.5 kg$\cdot$day exposure and 250 eVee threshold for AM analysis. The sensitive windows in $m_{\chi}$ are expanded by an order of magnitude to lower DM masses with Migdal effect incorporated. New limits on $\sigma_{\chi N}^{\rm SI}$ at 90\% confidence level are derived as $2\times$10$^{-32}\sim7\times$10$^{-35}$ $\rm cm^2$ for TI analysis at $m_{\chi}\sim$ 50$-$180 MeV/$c^2$, and $3\times$10$^{-32}\sim9\times$10$^{-38}$ $\rm cm^2$ for AM analysis at $m_{\chi}\sim$75 MeV/$c^2-$3.0 GeV/$c^2$.