Tibet Air Shower Array and the Muon Detector Array

This chapter presents details of the experiment used in this work, the Tibet air shower (AS) array and the muon detector (MD) array. The surface AS array covers a geometrical area of \(65,700\,\textrm{m}^2\) and captures extensive air showers initiated by primary particles to estimate their incoming directions and energies. The MD array with a geometrical area of \(3,400\,\textrm{m}^2\) installed underground counts the number of muons contained in air showers and discriminates CR- and gamma-ray-initiated showers. The stability of the data acquisition system and that of the gain of the signals of the AS detectors and MDs as well as the lengths of the cables used to transfer the signals of the AS detectors are monitored every 20 min during the data taking. On the other hand, the so-called probe calibration measures the transit time of the signals in the PMTs installed on the AS detectors. These calibration methods help us to remove instrumental biases included in the recorded data and reduce the systematic uncertainties in the estimation of the physical parameters of air showers and primary particles.