ALPACA air shower array to explore 100TeV gamma-ray sky in Bolivia

C. Calle, K. Hibino, N. Hotta, Y. Katayose, C. Kato, S. Kato, K. Kawata, W. Kihara, Y. Ko, H. Kojima, R. Mayta, P. Miranda, H. Mitsui, K. Munakata, H. Nakada, Y. Nakamura, M. Nishizawa, S. Ogio, M. Ohnishi, T. OhuraA. Oshima, M. Raljevich, H. Rivera, T. Saito, T. Sako, T. K. Sako, Y. Sengoku, S. Shibata, A. Shiomi, M. Subieta, N. Tajima, W. Takano, M. Takita, Y. Tameda, K. Tanaka, R. Ticona, H. Tsuchiya, Y. Tsunesada, S. Udo, K. Yagisawa, Y. Yokoe

Research output: Contribution to journalConference articlepeer-review


Andes Large area PArticle detector for Cosmic ray physics and Astronomy (ALPACA) is a new air shower array project as a collaboration between Bolivia and Japan to explore the 100 TeV gamma-ray sky in the southern hemisphere. In a plateau near the Chacaltaya mountain at 4,740 m altitude, a surface detector array covering 82,800 m2 with underground water Cherenkov muon detectors of total 5,400 m2 area will be constructed. Because of 2 m soil overburden, the muon detectors can detect muons of >1.2 GeV in air showers with a high purity. Using the conventional surface array to determine the primary energy and the arrival direction, the underground muon detectors improve the gamma/hadron separation and also mass identification of primary cosmic rays. For gamma-ray showers within zenith angle of 45 degrees, ALPACA has a full effective area above 20 TeV. At 20 TeV and 100 TeV, 99% and 99.9% hadron showers are rejected, respectively, while keeping the gamma-ray detection efficiency above 90%. Many interesting galactic objects can be observed with 0.2 degree angular resolution at 100 TeV with >2,000 hours/year exposure. ALPACA enables us the first sensitive survey of the southern gamma-ray sky at 100 TeV energy range that is crucial to identify PeV accelerating objects. Preparation for infrastructure and construction of a pathfinder array ALPAQUITA are ongoing. Scientific targets, expected performance of ALPACA including the prospects for some CR observations and current status are described.

Original languageEnglish
JournalProceedings of Science
StatePublished - 2019
Event36th International Cosmic Ray Conference, ICRC 2019 - Madison, United States
Duration: 24 Jul 20191 Aug 2019

Bibliographical note

Funding Information:
ALPACA is supported by the Japan Society for the Promotion of Science (JSPS) through Grants-in-Aid for Scientific Research (A) 19H00678, Scientific Research (B) 19H01922, and by the joint research program of the Institute for Cosmic Ray Research (ICRR), The University of Tokyo. KK is supported by the Toray Science Foundation.

Publisher Copyright:
© Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0).


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