Multipole analysis of IceCube data to search for dark matter accumulated in the Galactic halo

TL;DR

This paper introduces a multipole analysis method to detect large-scale anisotropies in neutrino data from IceCube, aiming to identify signals of dark matter annihilation in the Galactic halo, but finds no significant signal and sets new limits.

Contribution

The paper presents a novel multipole expansion technique with signal-specific weights to analyze neutrino arrival directions for dark matter signals in IceCube data.

Findings

No significant anisotropy detected in the data.

Set upper limits on dark matter self-annihilation cross-section.

Limits are comparable to gamma-ray constraints for high-mass dark matter.

Abstract

Dark matter which is bound in the Galactic halo might self-annihilate and produce a flux of stable final state particles, e.g. high energy neutrinos. These neutrinos can be detected with IceCube, a cubic-kilometer sized Cherenkov detector. Given IceCube's large field of view, a characteristic anisotropy of the additional neutrino flux is expected. In this paper we describe a multipole method to search for such a large-scale anisotropy in IceCube data. This method uses the expansion coefficients of a multipole expansion of neutrino arrival directions and incorporates signal-specific weights for each expansion coefficient. We apply the technique to a high-purity muon neutrino sample from the Northern Hemisphere. The final result is compatible with the null-hypothesis. As no signal was observed, we present limits on the self-annihilation cross-section averaged over the relative velocity distribution $<\sigma v>$ down to $1.9\cdot 10^{-23}\,\mathrm{cm}^3\mathrm{s}^{-1}$ for a dark matter particle mass of $700\,\mathrm{GeV}$ to $1000\,\mathrm{GeV}$ and direct annihilation into $\nu\bar{\nu}$. The resulting exclusion limits come close to exclusion limits from $\gamma$-ray experiments, that focus on the outer Galactic halo, for high dark matter masses of a few TeV and hard annihilation channels.