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

TL;DR

This study searches for bound states of charged dark matter particles with xenon in KamLAND-Zen, setting new upper limits on interaction cross sections and decay widths, but finds no evidence of such states.

Contribution

First experimental search for charged dark matter bound states using a liquid scintillator detector, establishing the most stringent upper limits on relevant parameters.

Findings

No significant events observed.

Set upper limits on recombination cross section times velocity.

Set upper limits on decay width of charged dark matter state.

Abstract

Particle dark matter could belong to a multiplet that includes an electrically charged state. WIMP dark matter ($\chi^{0}$) accompanied by a negatively charged excited state ($\chi^{-}$) 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 $m_{\chi^{0}} = 1$ TeV and mass difference $\Delta m = 17$ MeV, we set the most stringent upper limits on the recombination cross section times velocity $\langle\sigma v\rangle$ and the decay-width of $\chi^{-}$ to $9.2 \times 10^{-30}$ ${\rm cm^3/s}$ and $8.7 \times 10^{-14}$ GeV, respectively at 90% confidence level.