Search for dark matter annihilation in the center of the Earth with 8 years of IceCube data (1908.07255v1)

Abstract: Dark matter particles in the galactic halo can scatter off particles in celestial bodies such as stars or planets, lose energy and become gravitationally trapped. In this process, an accumulation of dark matter in the center of celestial bodies is expected, for example, at the center of the Earth. If dark matter self-annihilates into Standard Model particles, the end products of these annihilations include neutrinos. The IceCube Neutrino Observatory at the geographic South Pole can detect the resulting flux of neutrinos originating from dark matter annihilation in the center of the Earth. A search for this signal is on-going using 8 years of IceCube data and probing different annihilation channels. Here the sensitivities are presented for this new analysis, showing significant improvements with respect to the previous analyses from IceCube and other experiments.

• The paper demonstrates that 8 years of IceCube data significantly enhance the sensitivity to dark matter annihilation signals in Earth's core.
• It employs Monte Carlo simulations alongside a Boosted Decision Tree to effectively differentiate between signal neutrinos and atmospheric background.
• Results indicate a 3.8-fold improvement in sensitivity over previous studies, tightening constraints on WIMP interactions and guiding future analyses.

Search for Dark Matter Annihilation in the Center of the Earth with 8 Years of IceCube Data

The presented paper describes an investigation that leverages eight years of data from the IceCube Neutrino Observatory to search for neutrinos originating from potential dark matter (DM) annihilation within the Earth's core. This analysis focuses on detecting weakly interactive massive particles (WIMPs), hypothesized as potential DM candidates predominately in supersymmetric models.

Experimental Framework

IceCube, located at the South Pole, is a cubic kilometer neutrino detector array embedded in Antarctic ice. It consists of an extensive network of photomultiplier tubes arranged along 86 strings. These tubes detect the Cherenkov radiation emitted by relativistic particles produced from neutrino interactions, providing data concerning neutrino energy and trajectory. Within IceCube, a dense sub-array known as DeepCore improves sensitivity for low-energy neutrinos, extending the detection capacity below 100 GeV.

Dark Matter Detection Mechanism

WIMPs are purported to scatter off nuclei, lose energy, and become trapped by Earth’s gravitational field, potentially accumulating at the core. If WIMPs annihilate into Standard Model (SM) particles, the resultant interactions could produce neutrinos detectable by IceCube. This work aims to find evidence of such annihilations by analyzing the neutrino flux, contingent upon the mass and annihilation channels of the WIMPs.

Data Analysis and Methodology

The analysis utilizes Monte Carlo simulations to model background atmospheric muons and neutrinos, juxtaposed with signal simulations generated via the WimpSim software for various theoretical models of WIMP annihilation. The event selection process is refined through a Boosted Decision Tree (BDT), optimizing the discrimination between signal and background noise.

A binned likelihood approach, previously utilized by IceCube, estimates the sensitivity to the annihilation rate, $\Gamma_A$. This statistical methodology computes potential neutrino event distributions, helping establish constraints on the WIMP parameter space and providing sensitive bounds for observed neutrino-induced muons.

Results and Implications

The analysis significantly surpasses previous IceCube findings and other similar experiments, offering enhanced sensitivities for DM annihilation studies, especially for annihilation channels like $\chi\chi \rightarrow W^+W^-$ at a mass benchmark of $1$ TeV. The approach yields a sensitivity improvement by a factor of approximately 3.8 compared to previous limits.

Future Developments

This work sets the stage for subsequent analyses by adopting an unbinned, event-level likelihood framework that incorporates reconstructed energy data. Such advancements are expected to enhance the analytical sensitivity further. Continued refinement of these methodologies may strengthen limits on the interactive cross-section of DM-nucleon scattering, contributing to a finer understanding of DM properties and distribution.

Conclusion

This research demonstrates the progressive capability of the IceCube observatory in constraining WIMP interactions and refining compatibility with the DM framework, offering pivotal insights into potential sources of neutrinos resulting from DM processes. With ongoing enhancements, IceCube remains a critical tool in the search for elusive DM particle interactions, potentially contributing to broader astroparticle physics paradigms.