Search for charged excited states of dark matter with KamLAND-Zen

Particle dark matter could belong to a multiplet that includes an electrically charged state. WIMP dark matter ( χ 0 ) accompanied by a negatively charged excited state ( χ − ) 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 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 χ 0 = 1 TeV and mass difference Δ m = 17 MeV, we set the most stringent upper limits on the recombination cross section times velocity 〈 σ v 〉 and the decay-width of χ − to 9.2 × 10 − 30 c m 3 / s and 8.7 × 10 − 14 GeV, respectively at 90% confidence level.