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 (χ⁰) 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_χ0 = 1 TeV and mass difference Δm = 17 MeV, we set the most stringent upper limits on the recombination cross section times velocity (σv) and the decay-width of χ^- to 9.2×10^-30 cm³/s and 8.7×10^-14 GeV, respectively at 90% confidence level.