Fast Earth-Scattering Formalism Identifies Light Dark Matter via Dark Photon Mediators, Enabling Clear Discrimination of Strongly-Interacting Signals

The search for dark matter currently focuses on weakly interacting particles, but increasingly explores scenarios where dark matter interacts more strongly with ordinary matter. Agustín Lantero-Barreda, Carlos Centeno, Bradley J. Kavanagh, and colleagues at the Instituto de Física de Cantabria have developed a new method to accurately calculate how strongly interacting dark matter scatters within the Earth and atmosphere, a process that distorts the expected signal in direct detection experiments. Their semi-analytic formalism, implemented in the code Verne2, significantly speeds up these calculations, allowing for a more comprehensive exploration of possible dark matter properties. By accurately modelling both attenuation and reflection within the Earth, Verne2 achieves precision comparable to computationally intensive Monte Carlo simulations, while reducing calculation time dramatically and enabling detailed searches for the distinctive daily modulation signal expected from strongly interacting dark matter.

Dark matter can possess a large scattering cross section, potentially leading to significant interactions within the atmosphere and Earth before reaching a detector. This scattering distorts the expected dark matter signal and introduces a daily modulation, as the detector experiences varying levels of shielding from the Earth throughout the day. This modulation serves as a distinctive signature of strongly-interacting dark matter and offers a powerful means of distinguishing it from background noise. However, calculating these Earth-scattering effects using traditional methods is computationally intensive, hindering a systematic exploration of possible dark matter interactions. Scientists have now developed a semi-analytic formalism and accompanying code, Verne, to calculate these effects more efficiently, offering a faster approach to analysing potential dark matter signals.

Simulating Dark Matter Interactions with Verne

This work details the simulation and validation of a novel method, Verne, for calculating dark matter interactions in direct detection experiments. The core challenge in direct dark matter detection lies in accurately simulating both the expected signal and the unavoidable background noise. Direct detection experiments aim to observe the incredibly rare interactions between dark matter particles and ordinary matter within detectors, interactions expected to be extremely weak and easily masked. The authors focus on light dark matter candidates, those with masses below approximately 10 GeV, which are particularly difficult to detect due to the low energy they deposit within the detector.

Traditional simulation methods often struggle with these low-energy interactions, proving computationally expensive or inaccurate. Verne is a new code designed to efficiently and accurately simulate the response of detectors to these low-energy interactions, particularly focusing on the complex physics of nuclear recoils, when a dark matter particle bumps into an atomic nucleus. Accurate simulation is crucial for interpreting experimental results and setting limits on dark matter properties. The methodology involves developing Verne to calculate the expected recoil rate and energy spectrum of nuclear recoils induced by dark matter interactions, incorporating nuclear form factors, accurate nuclear recoil modeling, and a detailed representation of detector response.

The code underwent rigorous validation against analytical calculations, existing codes, and crucially, data from several direct detection experiments, including DAMIC-M and SENSEI. The results demonstrate that Verne accurately reproduces the results of analytical calculations and existing codes, and importantly, its predictions are consistent with the observed data from DAMIC-M and SENSEI. This provides strong evidence that Verne is a reliable tool for interpreting experimental results and improving sensitivity estimates. By accurately modeling both the signal and backgrounds, researchers can obtain more accurate estimates of the sensitivity of these experiments to different dark matter models.

Verne allows researchers to efficiently explore a wide range of dark matter parameters and identify regions of parameter space consistent with experimental data, handling complex effects such as multiple scattering, energy resolution limitations, and detector imperfections. This work has several important implications for the field of dark matter direct detection, providing a powerful tool for analyzing data from current and future experiments, constraining dark matter models, and optimizing detector design. The authors emphasize that Verne is an open-source code, making it accessible to the broader research community and promoting collaboration.

Earth Scattering Dominates MeV Dark Matter Signals

Scientists have developed a new semi-analytic formalism and accompanying code, Verne2, to calculate Earth-scattering effects on dark matter signals, significantly improving computational efficiency. This work addresses a key challenge in direct dark matter detection, particularly for models involving MeV-mass dark matter interacting via a dark photon mediator. The team’s formalism accurately models how dark matter particles scatter within the Earth and atmosphere before reaching detectors, distorting the expected signal and creating a distinctive daily modulation. This breakthrough delivers a substantial speedup in signal modeling, enabling faster and more comprehensive exploration of the dark matter parameter space. The team’s approach accurately calculates the daily modulation of the signal, a characteristic signature of strongly-interacting dark matter that provides a powerful method for discriminating against background noise. Tests prove that Verne2 is well-suited for performing detailed signal modeling in the search for this daily modulation, opening new avenues for direct dark matter detection experiments. The code, publicly available, allows researchers to efficiently evaluate the expected signals for a wide range of dark matter interactions and scattering cross sections.

Earth Scattering Simplifies Dark Matter Simulations

This work presents a new semi-analytic formalism and associated code, Verne2, for calculating the effects of Earth-scattering on dark matter signals. Researchers developed this method to address the computational challenges of simulating how dark matter interacts with the atmosphere and Earth, particularly for models involving low-mass dark matter interacting via a dark photon mediator. By approximating particle trajectories as straight lines between scattering events, and reflecting particles along their original path, the team achieved a significant reduction in computational cost, roughly a factor of 10,000, while maintaining accuracy. This advancement is crucial for systematically exploring the parameter space of dark matter models and interpreting data from current and future direct detection experiments. The authors acknowledge that the formalism relies on simplifying assumptions, such as neglecting energy loss during scattering, and that accuracy varies with detector location. Future work could refine these approximations and extend the method to more complex dark matter interactions.