ALPACA project to observe sub-PeV gamma-ray sky in the southern hemisphere

Though the maximum energy of the charged cosmic ray observations exceeds 100 EeV, the energy frontier of the gamma-ray observations is PeV. In the past years, Tibet ASγ, HAWC and LHAASO opened a new window of astronomy in the sub-PeV to PeV range, which is important to unveil yet unknown PeV cosmic accelerators in our galaxy. As these 3 experiments are all located in the northern hemisphere, observations in the southern hemisphere have been awaited. Andes Large area PArticle detector for Cosmic ray physics and Astronomy (ALPACA) is a new air shower array experiment under construction in the Bolivian Andes to explore the southern gamma-ray sky for the first time in this energy range. In this paper, we will provide an overview of the ALPACA project, including the initial observational results from a quarter-sized array named ALPAQUITA, which has been operating since 2023. A successful detection of the shadow of the moon, for example, validates the designed performance of the array. We will also outline the plan for the full-scale construction of ALPACA.