Identifying Extended PeVatron Sources via Neutrino Shower Detection

TL;DR

This paper proposes that neutrino shower detection, especially in water-based detectors, can identify extended PeVatron sources in the Milky Way, overcoming limitations of muon-track channels and aiding in cosmic-ray origin studies.

Contribution

It introduces the idea that all-flavor neutrino showers can detect extended PeVatron sources, highlighting a new search strategy for identifying cosmic-ray accelerators.

Findings

Shower channels have lower atmospheric background flux, improving detection prospects.

Extended sources may be missed in muon-track channels but detectable in shower channels.

Water-based detectors like KM3NeT can better resolve the directionality of neutrino showers.

Abstract

Identifying the Milky Way's very high energy hadronic cosmic-ray accelerators -- the PeVatrons -- is a critical problem. While gamma-ray observations reveal promising candidate sources, neutrino detection is needed for certainty, and this has not yet been successful. Why not? There are several possibilities, as we delineated in a recent paper [T. Sudoh and J. F. Beacom, Phys. Rev. D 107, 043002 (2023)]. Here we further explore the possibility that the challenges arise because PeVatrons have a large angular extent, either due to cosmic-ray propagation effects or due to clusters of sources. We show that while extended neutrino sources could be missed in the commonly used muon-track channel, they could be discovered in the all-flavor shower channel, which has a lower atmospheric-neutrino background flux per solid angle. Intrinsically, showers are quite directional and would appear so in water-based detectors like the future KM3NeT, even though they are presently badly smeared by light scattering in ice-based detectors like IceCube. Our results motivate new shower-based searches as part of the comprehensive approach to identifying the Milky Way's hadronic PeVatrons.