Speaker
Description
Andes Large-area PArticle detector for Cosmic-ray physics and Astronomy (ALPACA) is an air shower array experiment that aims to observe ultra-high-energy (UHE) gamma rays in the southern sky in 2027. It consists of a surface air shower array with a geometrical area of 83,000 ${\rm m}^2$ and a water Cherenkov-type muon detector array with a 2.0 ${\rm m}$ soil overburden covering an area of 3,600 ${\rm m}^2$. The prototype experiment called ALPAQUITA, a surface air shower array with an area of 18,000 ${\rm m}^2$, has been stably taking data since April 2023. The ALPAQUITA data is now being analyzed to validate the performance of the experiment and to study physics, such as the measurement of the cosmic-ray spectrum and the Forbush decrease due to large solar flares. Moreover, the muon detectors are under construction since November 2025; an extended prototype array equipped with a muon detector of a 900 ${\rm m}^2$ area will start the observation sensitive to UHE gamma rays in 2026. The presentation will detail the concept of our experiment, the current situation of the detector construction, and some results of the data analysis using the prototype experiment.
