Dark Matter-Induced Nuclear De-Excitation at SBND with Ab Initio Nuclear Theory

Abstract

We explore the sensitivity of the Short-Baseline Near Detector (SBND) experiment to light dark matter using MeV-scale electromagnetic activity. Inelastic scattering of dark matter with argon nuclei can excite nuclear states that subsequently de-excite via the emission of MeV-scale photons, producing localized low-energy "blip" signatures in a liquid argon time projection chamber. We perform state-of-the-art ab initio nuclear calculations, including all relevant argon excited states with energies up to 18 MeV, to provide reliable predictions for these signals. After accounting for relevant backgrounds, we find that SBND can probe previously unexplored regions of parameter space for light dark matter.

Figures (3)

• Figure 1: Feynman diagrams depicting (a) the production of $A^{'}$ via neutral meson two-body decay, (b) the production of $A^{'}$ through proton bremsstrahlung, and (c) the two-body decay of $A^{'}$ into a $\bar{\chi}$ and $\chi$ pair.
• Figure 2: DM fluxes with masses of (a) 1 MeV and (b) 100 MeV are shown at the front face of the SBND. Red, blue, and green lines correspond to DM production from $\pi^0$, $\eta$, and bremsstrahlung processes, respectively. Solid and dashed lines denote parent particles produced at the target and the dump, respectively. Uniform binning is applied to the x-axis in log-space, representing total DM energy. Thus, the y-axis shows counts per bin rather than counts per bin width. The total number of DM particles is calculated by summing the values for each bin, without multiplying by the bin widths. The red line ($\pi^0$ decay) is absent in (b) because $A^{'}$ has a greater mass than $\pi^0$, which prevents $\pi^0$ from decaying to produce $A^{'}$ on-shell. For these plots we consider, $\alpha_D=\frac{g_D^2}{4\pi}=0.5$, $m_{A^{'}}=3m_\chi$, and $\varepsilon=1.0$.
• Figure 3: Dark matter exclusion bounds at SBND obtained using ab initio nuclear calculations for the vector-portal dark photon model (left) and the leptophobic dark matter model (right), where $\alpha_B = {g_q^2 \over 4\pi}$. The assumed numbers of signal events are indicated in the legend.