Search for WIMP-${}^{129}$Xe inelastic scattering with particle identification in XMASS-I

Abstract

A search for Weakly Interacting Massive Particles (WIMPs) was conducted with the single-phase liquid-xenon detector XMASS through inelastic scattering in which ${}^{129}$Xe nuclei were excited, using an exposure ($327\mathrm{kg}\times 800.0\mathrm{days}$) 48 times larger than that of our previous study. The inelastic excitation sensitivity was improved by detailed evaluation of background, event classification based on scintillation timing that distinguished ${\hat{I}}^3$-rays and ${\hat{I}}^2$-rays, and simultaneous fitting of the energy spectra of ${\hat{I}}^3$-like and ${\hat{I}}^2$-like samples. No evidence of a WIMP signal was found. Thus, we set the upper limits of the inelastic channel cross section at 90\% confidence level, for example, $4.1\times 10^{-39}\mathrm{c}{\mathrm{m}}^2$ for a $200\mathrm{GeV}/c^2$ WIMP. This result provides the most stringent limits on the SD WIMP-neutron interaction and is better by a factor of 7.7 at $200\mathrm{GeV}/c^2$ than the existing experimental limit.

8 pages, 10 figures