Observation of large-scale anisotropy in the arrival directions of cosmic rays with LHAASO-KM2A

Abstract

A global large-scale anisotropy in the arrival directions of cosmic rays were observed both in the Northern and Southern Hemisphere. It is evident that the morphology of the large-scale anisotropy and magnitude is energy dependent. However, only a few experiments can up to PeV with long term data accumulation. The measurement of anisotropy at high energies can provide more clues to the origin and propagation of cosmic rays. The Large High Altitude Air Shower Observatory (LHAASO), covering an area of 1.36 square kilometer, detect cosmic rays from sub-TeV up to 100 PeV with good element discrimination ability. In this paper, data collected by half array of KM2A during 2020 is used to analyze the anisotropy. The anisoptropies from 23 TeV up to 985 TeV are reported. The "inverse" anisotropy is observed at 985 TeV with significance of 5σ. The evolution of the anisotropy with energy is consistent with the others. With the operation of LHAASO, more accurate observation for the cosmic-ray anisotropy at higher energy will be made.