# DaMaSCUS: The Impact of Underground Scatterings on Direct Detection of Light Dark Matter

## TL;DR

This paper introduces DaMaSCUS, a Monte Carlo simulation tool that models how underground scatterings affect the detection of light, strongly interacting dark matter, impacting recoil spectra and diurnal modulation signals.

## Contribution

The paper presents a novel publicly available simulation code that accurately models underground scatterings of dark matter, accounting for their effects on detection signals and diurnal modulation.

## Key findings

- Underground scatterings significantly alter dark matter recoil spectra.
- The simulation predicts diurnal modulation patterns in detection signals.
- Earth shadowing effects depend on detector depth and location.

## Abstract

Conventional dark matter direct detection experiments set stringent constraints on dark matter by looking for elastic scattering events between dark matter particles and nuclei in underground detectors. However these constraints weaken significantly in the sub-GeV mass region, simply because light dark matter does not have enough energy to trigger detectors regardless of the dark matter-nucleon scattering cross section. Even if future experiments lower their energy thresholds, they will still be blind to parameter space where dark matter particles interact with nuclei strongly enough that they lose enough energy and become unable to cause a signal above the experimental threshold by the time they reach the underground detector. Therefore in case dark matter is in the sub-GeV region and strongly interacting, possible underground scatterings of dark matter with terrestrial nuclei must be taken into account because they affect significantly the recoil spectra and event rates, regardless of whether the experiment probes DM via DM-nucleus or DM-electron interaction. To quantify this effect we present the publicly available Dark Matter Simulation Code for Underground Scatterings (DaMaSCUS), a Monte Carlo simulator of DM trajectories through the Earth taking underground scatterings into account. Our simulation allows the precise calculation of the density and velocity distribution of dark matter at any detector of given depth and location on Earth. The simulation can also provide the accurate recoil spectrum in underground detectors as well as the phase and amplitude of the diurnal modulation caused by this shadowing effect of the Earth, ultimately relating the modulations expected in different detectors, which is important to decisively conclude if a diurnal modulation is due to dark matter or an irrelevant background.