First Nuclear Ultra-Heavy Dark Matter Search in Argon Time Projection Chambers with the DarkSide-50 Experiment

TL;DR

This work reports the first search for nuclear ultra-heavy dark matter (UHDM) using the DarkSide-50 dual-phase liquid argon TPC. UHDM is modeled as composite dark nuclei with mass $M_χ$, radius $R_χ$, and a cross section $σ_{χ,n}$ for elastic scattering, incorporating form factors $F_χ$ and $F_N$ and the regime-dependent coherence controlled by $qR_χ$. The analysis accounts for Earth's overburden via the Verne toolkit and targets multi-scatter energy-deposition signatures, focusing on S1 scintillation signals in a 532-day underground data set with ROI 100–8000 PE. No UHDM signal is observed, and 90% CL exclusions are derived for $m_χ ∈ igl\\{10,50,100,500\igr\ ext{ GeV}/c^2}$, detailing how the composite nature and overburden effects shape sensitivity. The results establish a new UHDM-search regime in liquid-argon detectors and provide a framework for future exploration of dark-nucleon mass and cross-section parameter space.

Abstract

We report the first search for nuclear ultra-heavy dark matter (UHDM) in a dual-phase liquid argon time projection chamber using the DarkSide-50 experiment. Unlike conventional weakly interacting massive particles (WIMPs), nuclear UHDM candidates may be composed of many dark nucleons and scatter numerous times while passing through the detector. Accounting for energy loss through the Earth's overburden, we apply selection criteria optimized for multi-scatter event topologies using the 532-day low-radiation campaign of the DarkSide-50 detector. Excluded limits on the UHDM-nucleon scattering cross section for dark nucleon masses of $m_χ= 10, 50, 100, 500 \, \mathrm{GeV/c^2}$ are presented.

Figures (9)

• Figure 1: Average number of energy deposits for UHDM of different $\sigma_{\chi,n}$.The left-hand (blue) axis shows the number of energy deposits, and the right-hand (purple) shows the time between energy deposits. The dashed line represents the average UHDM transit time.
• Figure 2: The product $qR_{\chi}$ as a function of $M_{\chi}$ and $m_{\chi}$. The red line shows where $qR_{\chi}$ = 1; at higher values, coherent scatter tends to be suppressed.
• Figure 3: Energy deposited in the parameter space region of interest, for dark nucleon mass $m_{\chi} = 10 \mathrm{\,GeV/c^2}$. The red region estimates undetectable parameter space due to overburden effects as predicted in Coskuner. The gray region delimits area where the scattering cross section $\sigma_{\chi,n}$ is larger than the geometrical cross section $\sigma_{\mathrm{geo}}$, which depends on the dark nucleon mass $m_{\chi}$.
• Figure 4: Velocity distribution in the detector rest frame for a UHDM candidate of $M_{\chi}=10^{7}\,\mathrm{GeV/c^2}$ and $\sigma_{\chi,n}=10^{-27}\,\mathrm{cm^2}$ for different incoming directions with respect to the detector's vertical axis ($\gamma)$. Darker colors represent candidates traveling the shortest path to the detector, while lighter colors represent candidates traveling through most of Earth's overburden before reaching the detector.
• Figure 5: Differential probability per unit recoil energy for $m_{\chi}=10 \,\mathrm{GeV/c^2}$, $M_{\chi} = 10^7 \,\mathrm{GeV/c^2}$, and $\sigma_{\chi,n}=10^{-27} \, \mathrm{cm^2}$.