- Abe, S;
- Eizuka, M;
- Futagi, S;
- Gando, A;
- Gando, Y;
- Goto, S;
- Hachiya, T;
- Hata, K;
- Hosokawa, K;
- Ichimura, K;
- Ieki, S;
- Ikeda, H;
- Inoue, K;
- Ishidoshiro, K;
- Kamei, Y;
- Kawada, N;
- Kishimoto, Y;
- Koga, M;
- Kurasawa, M;
- Mitsui, T;
- Miyake, H;
- Morita, D;
- Nakahata, T;
- Nakajima, R;
- Nakamura, K;
- Nakamura, R;
- Nakamura, R;
- Nakane, J;
- Ozaki, H;
- Sakai, T;
- Shimizu, I;
- Shirai, J;
- Shiraishi, K;
- Shoji, R;
- Suzuki, A;
- Takeuchi, A;
- Tamae, K;
- Watanabe, H;
- Watanabe, K;
- Obara, S;
- Yoshida, S;
- Umehara, S;
- Fushimi, K;
- Kotera, K;
- Urano, Y;
- Ichikawa, A;
- Berger, BE;
- Fujikawa, BK;
- Learned, JG;
- Maricic, J;
- Axani, SN;
- Fu, Z;
- Smolsky, J;
- Winslow, LA;
- Efremenko, Y;
- Karwowski, HJ;
- Markoff, DM;
- Tornow, W;
- Dell'Oro, S;
- O'Donnell, T;
- Detwiler, JA;
- Enomoto, S;
- Decowski, MP;
- Weerman, KM;
- Grant, C;
- Li, A;
- Song, H
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 mχ0=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.