Observation of the galactic cosmic ray moon shadowing effect with the ARGO-YBJ experiment

Cosmic rays are hampered by the Moon and a deficit in its direction is expected (the so-called Moon shadow). The Moon shadow is an important method to determine the performance of an air shower array. In fact, the westward displacement of the shadow center, due to the propagation of cosmic rays in the geomagnetic field, allows to calibrate the energy scale of the primary particles observed by the detector. In addition, the shape of the shadow allows a measurement of the angular resolution and the position of the deficit at high energy allows the evaluation of the pointing accuracy of the detector. In this paper we present the observation of the galactic cosmic rays Moon shadowing effect performed by the ARGO-YBJ experiment in the multi- TeV energy region. The measured angular resolution as a function of the shower size is compared with the expectations from a MC simulation.