LHAASO and the origin of cosmic rays

The extension of the cosmic ray spectrum beyond 1 PeV (1 PeV = 1015 eV) indicates the existence of particle accelerators operating as PeVatrons in the Milky Way. However, recent gamma-ray observations reveal that supernova remnants (SNRs), considered the major source of galactic cosmic rays, have difficulty in accelerating cosmic rays to PeV. Therefore, searching and identifying PeVatrons is crucial for understanding the origin of cosmic rays. The ultra-high-energy (UHE) gamma-ray observations will provide decisive evidence for such studies. Due to its high sensitivity in the UHE gamma-ray band, Large High Altitude Air Shower Observatory (LHAASO) would play a key role in the research on PeVatron. After running the 1/2 LHAASO-KM2A array, 12 UHE gamma-ray sources were detected. This paper summarizes the observation results and discusses the prospect of the full LHAASO array.