What question did this study set out to answer?

The aim is to investigate the transport mechanism of very high-energy cosmic rays using diffuse gamma ray and neutrino backgrounds.

February 5, 2026

The origin of very high-energy diffuse

Key Points

The aim is to investigate the transport mechanism of very high-energy cosmic rays using diffuse gamma ray and neutrino backgrounds.
Analyzed diffuse gamma ray measurements from LHAASO in the ∼TeV − PeV range.
Investigated the very high-energy diffuse neutrino background from IceCube.
Compared cosmic ray ratios to identify energy-independent grammage in specific regions.
Found an approximately energy independent grammage of X ∼ 0.4 g cm−2 in certain cosmic ray regions.
Identified that gamma rays and neutrinos are produced with a hard spectrum resembling the source spectrum.
Speculated on the presence of cocoons where cosmic rays spend ∼0.3 million years before entering the Galactic environment.

Abstract

The secondary/primary cosmic-ray ratios and the diffuse backgrounds of gamma rays and neutrinos provide us with complementary information about the transport of Galactic cosmic rays (CRs). We used the recent measurement of the diffuse gamma ray background in the ∼TeV − PeV range by LHAASO and of the very high-energy diffuse neutrino background from the Galactic disc by IceCube to show that CRs may be accumulating an approximately energy independent grammage X ∼ 0.4 g cm−2, in regions where gamma rays and neutrinos are produced with a hard spectrum, resembling the source spectrum. We speculate that this grammage reflects the early stages of cosmic ray transport around sources, in what are referred to as cocoons, where particles spend ∼0.3 Myr before starting their journey in the Galactic environment.

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