Improved Gamma-Hadron Separation for PeV Photon Searches with IceCube (ICRC 2025)

TL;DR

This paper presents an improved method for distinguishing gamma-ray induced air showers from hadronic showers in IceCube, significantly enhancing the sensitivity for PeV photon source searches by leveraging combined surface and deep detector data.

Contribution

The study introduces a new gamma-hadron separation technique using IceTop and IceCube data, achieving over 1000-fold background suppression at PeV energies.

Findings

Gamma-hadron separation better than 10^{-3} at PeV energies.

Suppression of hadronic background exceeds 1000 times compared to photon-induced showers.

Enhanced sensitivity extends the energy range for PeV photon searches.

Abstract

IceTop, the km$^2$ surface array of the IceCube Neutrino Observatory at the South Pole, is sensitive to air showers of all primary particles, including gamma rays. In particular, in the PeV energy range, the combination of IceTop and IceCube's deep optical detector provides excellent gamma-hadron separation. Almost all air showers induced by cosmic-ray protons and heavier nuclei in this energy range contain high-energy muons detectable by the deep detector, while most photon-induced air showers do not. Therefore, IceCube's deep detector can be used to strongly suppress hadronic background in photon searches. Furthermore, the lateral distribution of the air-shower signal in IceTop provides additional gamma-hadron separation. In the PeV energy range, the gamma-hadron separation achieved is better than $10^{-3}$: air-shower events measured with IceCube are suppressed more than 1000 times stronger than photon-induced showers of the same energy simulated with Sibyll 2.3d. This improved gamma-hadron separation in combination with an extension of the energy range to lower energies provides discovery potential for future searches for PeV photon sources in IceCube's field of view.