Constraints on inelastic dark matter from the CDEX-1B experiment

Abstract

We present limits on spin-independent inelastic weakly interacting massive particles (WIMP)-nucleus scattering using the 737.1 kg$\cdot$day dataset from the CDEX-1B experiment. Expected nuclear recoil spectra for various inelastic WIMP masses $m_{\chi }$ and mass splittings $\delta$ are calculated under the standard halo model. An accurate background model of CDEX-1B is constructed by simulating all major background sources. The model parameters are then determined through maximum likelihood estimation and Markov chain Monte Carlo fitting. The resulting 90\% confidence level upper limits on the WIMP-nucleon cross section ${\sigma }_{\mathrm{n}}$ exclude certain DAMA/LIBRA allowed regions: the ${\chi }^2<4$ regions for $\delta <30$ keV at $m_{\chi }=250$ GeV and the ${\chi }^2<9$ region for $\delta <50$ keV at $m_{\chi }=500$ GeV. The method is applicable to other inelastic dark matter scenarios, and the upcoming CDEX-50 experiment is expected to improve sensitivity by four orders of magnitude.

Comments: 10 pages, 8 figures. Version updated to match PRD version