The performance of the LHAASO-KM2A tested by the cosmic-ray Moon shadow

Abstract

The KM2A is a major ground-based array for the researches on cosmic rays around the “knee” region and the ultra high energy gamma-ray astronomy, which depends heavily on its performance. The half array of the KM2A has been operated from December 27, 2019 to November 30, 2020. The cosmic ray Moon shadow, which moves between ±25◦ of declination and is observed with significance up to -25 standard deviation each month, is used as an unique and powerful source to test the array’s performance. Through the observation of the characteristics of the Moon shadow, including the position displacement, shape, deficit, and their variation with the time and energy, we test the pointing error, angular resolution, long-term stability of the KM2A and the absolute energy scale of the primary cosmic-ray particles. In particular, the pointing errors for showers from different declinations are discussed in this work.