Deconstructive Composite Dark Matter Detection

TL;DR

This work tackles the detection of loosely bound composite dark matter that disassembles as it traverses the Earth. It develops analytic and numerical methods to model constituent cascades, quantifying the surface cascade spread $R_{sp}$ and predicting multi-scatter, time-delayed signatures within underground detectors, as well as possible correlated signals in distant labs. The results show that such cascades can yield non-collinear scatters and sizeable timing separations, enabling new multiscatter search strategies, while cosmological dissociation remains negligible ($f_{free} \lesssim 10^{-10}$). These findings expand terrestrial DM detection prospects by highlighting a rich phenomenology for composite states and motivating detector-wide, time- and location-aware analyses.

Abstract

We investigate the detection of composite dark matter that disassembles into a cascade while crossing the Earth. This occurs for loosely bound composite dark matter, where the binding energy per constituent is small, such that scattering with Standard Model nuclei typically imparts enough energy to dissociate a constituent from its composite. Trajectories and cascade profiles are found for dissociated constituents that are further diverted by scattering through the Earth. Such scattering cascades are a common feature of TeV-scale weakly-interacting dark matter loosely bound in composites. We identify underground detector signatures of constituent cascades that depend on composite characteristics; these signatures include non-collinear multiple scatters in detectors, parameter-dependent timing separation of multiscatter events, and regions of parameter space where a dark matter cascade would leave a coincident signature in different underground laboratories.

Figures (10)

• Figure 1: Diagram of a loosely bound dark matter composite entering the Earth, and its subsequent disassembly. The disassembled constituents exit Earth with a spatial spread on the Earth's surface $R_{sp}$.
• Figure 2: Top: Analytical estimates (Eq. \ref{['eq:AnalyticalR']}) of the constituent spread radius on the Earth's surface $R_{sp}^{(N_s)}$, in log scale, varying constituent mass $m_d$ and constituent-nucleon cross-section $\sigma_{nd}$, for two entry angles $\theta_e = {0,40}^\circ$. Bottom left: Constituent spread radius $R_{Sp}^{(Sim)}$ averaged over flux-weighted entry angle $\theta_e$, using numerical trajectory simulations described in Section \ref{['sec:modelling']}. Bottom right: Example simulated trajectories of $10^3$ dissociated constituents traversing the Earth, for fixed values of constituent mass $m_d$, constituent-nucleon cross-section $\sigma_{nd}$, and entry angles. The final constituent positions upon exiting the Earth are plotted as red points. The Earth's surface$+$mantle and core are respectively shown as green and red spheres.
• Figure 3: Left: The Earth's density as a function of radius from the Earth's centre, according to the Preliminary Reference Earth Model (PREM) Dziewonski:1981xy. Right: The average local mean free path of a dark matter particle of mass $m_d = 1$ TeV in the Earth, as a function of radius, calculated from the local Earth density and composition, assuming a spin-independent nucleon scattering cross-section $\sigma_{nd}$ for constituent dark matter particles.
• Figure 4: Flowchart showing the numerical method used in DarkDisassembly to model composite dark matter constituent particles disassembling as they traverse the Earth's interior.
• Figure 5: Direct detection constraints and prospects for disassembling composite dark matter, for constituent mass $m_d$ and constituent-nucleon cross-section $\sigma_{nd}$. The regions to the left of the purple lines marked for $N_D=10^{18}-10^{6}$ constituents are estimated exclusions for single scatter searches at experiments like LUX-ZEPLIN (LZ), XENON-NT and PANDA-X, and DEAP-3600, which would have seen single scatter dark matter events given the spread of constituents. We calculate these estimated exclusions by assuming a target volume of a cubic metre of liquid xenon of density $3.52$ g/cm$^3$ with a year observation time. The regions to the right of these purple lines require new multiscatter searches discussed in the text, because a typical cascade produces multiple coincident recoils in underground detectors. For comparison, the solid red line shows the published constraint on spin-independent dark matter from LZ, extrapolated to higher dark matter masses Aalbers_2025. The teal dashed contours, which are often coincident with the purple single scatter bounds, indicate the separation between parameter space for single-scattering vs multi-scattering due to DM cascades, for constituent number $N_D$ indicated. The green shaded region delineates the Earth attenuation region, where at least 50% of the individual constituents have lost more than 90% of their energy due to scattering in the Earth before reaching the detector.