New Limits on Interactions between Weakly Interacting Massive Particles and Nucleons Obtained with CsI(Tl) Crystal Detectors

TL;DR

This paper reports new experimental limits on WIMP-nucleon interactions using CsI(Tl) detectors, setting the most stringent constraints for certain WIMP masses and challenging some dark matter models.

Contribution

It provides the first limits on WIMP interactions from CsI(Tl) detectors with a large exposure, including spin-dependent scattering constraints for WIMPs over 20 GeV/c2.

Findings

No nuclear recoils detected above background.

Set upper limits on WIMP interaction rates from 3 to 11 keV.

Most stringent limits on spin-dependent WIMP-proton scattering for masses >20 GeV/c2.

Abstract

New limits are presented on the cross section for Weakly Interacting Massive Particle (WIMP) nucleon scattering in the KIMS CsI(T) detector array at the Yangyang Underground Laboratory. The exposure used for these results is 24524.3 kg\cdotdays. Nuclei recoiling from WIMP interactions are identified by a pulse shape discrimination method. A low energy background due to alpha emitters on the crystal surfaces is identified and taken into account in the analysis. The detected numbers of nuclear recoils are consistent with zero and 90% confidence level upper limits on the WIMP interaction rates are set for electron equivalent energies from 3 keV to 11 keV. The 90% upper limit of NR event rate for 3.6-5.8 keV corresponding to 2-4 keV in NaI(T) is 0.0098 counts/kg/keV/day which is below the annual modulation amplitude reported by DAMA. This is incompatible with interpretations that enhance the modulation amplitude such as inelastic dark matter models. We establish the most stringent cross section limits on spin-dependent WIMP-proton elastic scattering for the WIMP masses greater than 20 GeV/c2.