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

We report results on the searches of weakly interacting massive particles (WIMPs) with sub-GeV masses (m_χ) 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 day exposure and 160 eVee threshold for TI analysis, and 1107.5 kg day exposure and 250 eVee threshold for AM analysis. The sensitive windows in m_χ are expanded by an order of magnitude to lower DM masses with Migdal effect incorporated. New limits on σ_χNSI at 90% confidence level are derived as 2×10^-32~7×10^-35 cm² for TI analysis at m_χ~50--180 MeV/c², and 3×10^-32~9×10^-38 cm² for AM analysis at m_χ~75 MeV/c²--3.0 GeV/c².