Search for Spatial Correlations of Neutrinos with Ultra-High-Energy Cosmic Rays

TL;DR

This study investigates potential spatial correlations between ultra-high-energy cosmic rays and high-energy neutrinos using multiple analysis methods, but finds no significant excess, thereby constraining the neutrino flux associated with cosmic rays.

Contribution

It presents three novel approaches to correlate neutrino and cosmic ray arrival directions with improved data and analysis techniques, refining previous results from 2015.

Findings

No significant spatial correlations were detected.

Over-fluctuations observed previously are now reduced.

Results place tighter constraints on neutrino flux linked to cosmic rays.

Abstract

For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data is provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above $\sim$50 EeV is provided by the Pierre Auger Observatory and the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrinos clustering in the vicinity of UHECR directions. The second analysis searches for an excess of UHECRs in the direction of the highest-energy neutrinos. The third analysis searches for an excess of pairs of UHECRs and highest-energy neutrinos on different angular scales. None of the analyses has found a significant excess, and previously reported over-fluctuations are reduced in significance. Based on these results, we further constrain the neutrino flux spatially correlated with UHECRs.