ALPACA experiment: A new air shower array to explore the sub-PeV gamma-ray sky in the southern hemisphere

Abstract

In the last few years, gamma-ray astronomy opens a new window in the sub-PeV to PeV range inaugurated by the Tibet AS𝛾 collaboration followed by the HAWC and LHAASO collaborations. The successful three experiments are located in the northern hemisphere and they are not able to study the southern sky where potential interesting objects are known to exist. Andes Large area PArticle detector for Cosmic ray physics and Astronomy (ALPACA) is a project to cover the southern sub-PeV to PeV sky using a new air shower array at the plateau of the Chacaltaya mountain at the altitude of 4,740 m in Bolivia. The prime target of ALPACA is to reveal PeV cosmic-ray accelerators presumably existing in the galactic plane, including the galactic center. A prototype array ALPAQUITA consisting of 97 surface counters and 900 m$^2$ muon detectors is now under construction and planned to partly start data taking in 2022. The extension to the 401 counters and 3,700 m$^2$ muon detectors is scheduled in 2024. In this contribution, a general introduction to ALPACA, the current status of ALPAQUITA, and an extension plan after 2023 are presented.