Precise measurements of the cosmic ray proton energy spectrum in the "knee'' region

TL;DR

This paper presents precise measurements of the cosmic ray proton energy spectrum in the 0.15 to 12 PeV range, revealing spectral features that suggest a new component related to Galactic cosmic ray origins.

Contribution

It provides the first high-purity, spectroscopic measurement of the proton spectrum in the knee region using LHAASO, with results comparable to satellite data at lower energies.

Findings

Proton spectrum hardens and then softens around 3 PeV.

Spectral features indicate a new cosmic ray component.

Results support the link between PeVatrons and the knee in the spectrum.

Abstract

We report the high-purity identification of cosmic-ray (CR) protons and a precise measurement of their energy spectrum from 0.15 to 12 PeV using the Large High Altitude Air Shower Observatory (LHAASO). Abundant event statistics, combined with the simultaneous detection of electrons/photons, muons, and Cherenkov light in air showers, enable spectroscopic measurements with statistical and systematic precision comparable to satellite data at lower energies. The proton spectrum shows significant hardening relative to low-energy extrapolations, culminating at 3 PeV, followed by sharp softening. This distinct spectral structure closely aligned with the knee in the all-particle spectrum points to the emergence of a new CR component at PeV energies that might be linked to the dozens of PeVatrons recently discovered by LHAASO, and offers crucial clues to the origin of Galactic cosmic rays.