Search for Charged Excited States of Dark Matter with KamLAND-Zen

Abstract

Particle dark matter could belong to a multiplet that includes an electrically charged state. WIMP dark matter ($\ddot{I}{‡}^0$) accompanied by a negatively charged excited state ($\ddot{I}{‡}^{-}$) with a small mass difference (e.g. $<$ 20 MeV) can form a bound-state with a nucleus such as xenon. This bound-state formation is rare and the released energy is $\mathcal{O}(1-10$) MeV depending on the nucleus, making large liquid scintillator detectors suitable for detection. We searched for bound-state formation events with xenon in two experimental phases of the KamLAND-Zen experiment, a xenon-doped liquid scintillator detector. No statistically significant events were observed. For a benchmark parameter set of WIMP mass $m_{\ddot{I}{‡}^0}=1$ TeV and mass difference $\hat{I}”m=17$ MeV, we set the most stringent upper limits on the recombination cross section times velocity $⟨\ddot{I}ƒv⟩$ and the decay-width of $\ddot{I}{‡}^{-}$ to $9.2\times 10^{-30}$ $\mathrm{c}{\mathrm{m}}^3/s$ and $8.7\times 10^{-14}$ GeV, respectively at 90% confidence level.