Detecting light dark matter with prompt-delayed events in neutrino experiments

Abstract

We demonstrate the prompt-delayed signals induced by knockout neutrons from the quasi-elastic scattering in neutrino experiments provides a new avenue for detecting light dark matter. As an illustration, we consider the detection of atmospheric dark matter in the liquid scintillator detectors. The results show that the constraint on the DM-nucleon interaction from KamLAND is approximately one order of magnitude more stringent than those obtained from the elastic nuclear recoil signals in dark matter direct detection experiments. Furthermore, a larger volume neutrino experiment, such as JUNO, is expected to significantly enhance the light dark matter detection sensitivity through the quasi-elastic scattering.

Figures (3)

• Figure 1: A sketch of the quasi-elastic scattering of a relativistic DM with a carbon nucleus in the liquid scintillator detector of neutrino experiment, $\chi + A \rightarrow \chi +(A-1)^{\star} + n$. The knockout neutron will lead to the prompt signal through the elastic scattering process, $n + p \to n + p$, where the recoiling proton emits scintillation light as it passes through medium. The delayed signal is caused by the radiative capture of knockout neutron, $n+p\to d + \gamma$, emitting 2.2 $\mathrm{MeV}\ \gamma$-ray. Besides, the excited residual nucleus can also produce an observable signal through its de-excitation.
• Figure 2: Left: The expected counts in 3--MeV bins for $m_\chi = 0.1$ MeV DM with energy $E_\chi = 0.2, 0.4, 0.6, 0.8$ GeV. Right: The expected differential deposited energy spectrum of the prompt signals for the QES of DM-nucleus at $m_\chi = 1, 10, 100$ MeV. In both plots, we take $\bar{\sigma}_n \simeq 1\times 10^{-33}$ cm$^{2}$ and $m_S = 0.3$ GeV.
• Figure 3: 90% C.L. limits on the spin-independent atmospheric DM-nucleon scattering cross section versus the DM mass $m_\chi$. The QES limits from KamLAND and a projection for the upcoming JUNO are shown in blue and the red lines, respectively. Other exclusion limits derived from ES processes are plotted by dashed lines [ LUX (orange), XENONnT (black), and PandaX-4T (green)]. Here $m_S = 300$ MeV and BR$(\eta \to \pi \chi \bar{\chi})\ \simeq \ 1\times 10^{-5}$.