A Search for Charged Excitation of Dark Matter with the KamLAND-Zen Detector

Author(s): Abe, S; Asami, S; Gando, A; Gando, Y; Gima, T; Goto, A; Hachiya, T; Hata, K; Hayashida, S; Hosokawa, K; Ichimura, K; Ieki, S; Ikeda, H; Inoue, K; Ishidoshiro, K; Kamei, Y; Kawada, N; Kinoshita, T; Koga, M; Maemura, N; Mitsui, T; Miyake, H; Nakamura, K; Nakamura, K; Nakamura, R; Ono, A; Ota, N; Otsuka, S; Ozaki, H; Sakai, T; Sambonsugi, H; Shimizu, I; Shirahata, Y; Shirai, J; Shiraishi, K; Suzuki, A; Suzuki, Y; Takeuchi, A; Tamae, K; Ueshima, K; Wada, Y; Watanabe, H; Yoshida, Y; Obara, S; Chernyak, D; Kozlov, A; Yoshida, S; Umehara, S; Takemoto, Y; Fushimi, K; Hirata, S; Ichikawa, A; Nakamura, KZ; Yoshida, M; Berger, BE; Fujikawa, BK; Grant, C; Li, A; Learned, JG; Maricic, J; Axani, S; Winslow, LA; Fu, Z; Efremenko, Y; Karwowski, HJ; Markoff, DM; Tornow, W; ODonnell, T; DellOro, S; Detwiler, JA; Enomoto, S; Decowski, MP | Abstract: There are many theories where a dark matter particle is part of a multiplet with an electrically charged state. If WIMP dark matter ($\chi^{0}$) is accompanied by a charged excited state ($\chi^{-}$) separated by a small mass difference, it can form a stable bound state with a nucleus. In supersymmetric models, the $\chi^{0}$ and the $\chi^{-}$ could be the neutralino and a charged slepton, such as the neutralino-stau degenerate model. The formation binding process is expected to result in an energy deposition of {\it O}(1--10 MeV), making it suitable for detection in large liquid scintillator detectors. We describe new constraints on the bound state formation with a xenon nucleus using the KamLAND-Zen 400 Phase-II dataset. In order to enlarge the searchable parameter space, all xenon isotopes in the detector were used. For a benchmark parameter set of $m_{\chi^{0}} = 100$ GeV and $\Delta m = 10$ MeV, this study sets the most stringent upper limits on the recombination cross section $\langle\sigma v\rangle$ and the decay-width of $\chi^{-}$ of $2.0 \times 10^{-31}$ ${\rm cm^3/s}$ and $1.1 \times 10^{-18}$ GeV, respectively (90\% confidence level).