Search for WIMP-129Xe 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 129Xe nuclei were excited, using an exposure (327 kg × 800.0 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 γ-rays and β-rays, and simultaneous fitting of the energy spectra of γ-like and β-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 × 10 − 39 cm 2 for a 200 GeV/c2 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 GeV/c2 than the existing experimental limit.