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Andes Large-area PArticle detector for Cosmic-ray physics and Astronomy (ALPACA) is an international experiment that applies southern very-high-energy (VHE) gamma-ray astronomy to determine the origin of cosmic rays around the knee energy region ($10^{15}\, {\rm eV} - 10^{16}\, {\rm eV}$). The experiment consists of an air shower (AS) array with a surface of $83, 000\, {\rm m}^2$ and an underground water Cherenkov muon detector (MD) array covering $5, 400\, {\rm m}^2$. The experimental site is at the Mt. Chacaltaya plateau in La Paz, Bolivia, with an altitude of $4, 740\, {\rm m}$ corresponding to $572\, {\rm g}/{\rm cm}^2$ atmospheric thickness. As the prototype experiment of ALPACA, the ALPAQUITA experiment aims to begin data acquisition in late 2021. The ALPAQUITA array consists of a smaller AS array ($18, 450\, {\rm m}^2$) and underground MD ($900\, {\rm m}^2$), which are now under construction. ALPAQUITA's sensitivity to gamma-ray sources is evaluated with Monte Carlo simulations. The simulation finds that five gamma-ray sources observed by H.E.S.S. and HAWC experiments will be detected by ALPAQUITA beyond 10 TeV and one out of these five - HESS J1702-420A - above 300 TeV in one calendar year observation. The latter finding means that scientific discussions can be made on the emission mechanism of gamma rays beyond 100 TeV from southern sources on the basis of the observational results of this prototype experiment., This is the manuscript accepted by Experimental Astronomy. For the published article, see https://doi.org/10.1007/s10686-021-09796-8

The ALPACA experiment is a new air shower experiment mainly aiming to explore the southern sky in the VHE gamma-ray regime beyond 100 TeV. As the prototype experiment, ALPAQUITA will start in late 2021. It consists of a surface air shower array (18,450 ${\rm m}^2$) and an underground muon detector array (900 ${\rm m}^2$). In this study, the performance of ALPAQUITA including the sensitivity to gamma-ray point sources is investigated using a Monte Carlo simulation to quantitatively evaluate the possibility of detection of gamma-ray sources in the prototype phase. Corsika 7.6400 and Geant4 v10.04.p02 are used to simulate air shower development in the atmosphere and detector response, respectively. The output data are then processed and analyzed in the same way as the experiment. As a result, the study finds that the air shower array has an energy resolution of $\pm21\%$ and the angular resolution of $\simeq 0.2^{\circ}$ for gamma rays with an energy of 100 TeV. The detection area of the air shower array for gamma rays reaches $\simeq 12, 600 \, {\rm m}^2$ above $\simeq 10\, {\rm TeV}$. The muon detector rejects $\simeq 99.9\%$ of background cosmic rays and maintains $\simeq 80\%$ of signal gamma rays. This high discrimination power will enable the detection of five southern known gamma-ray sources beyond 30 TeV and the extension of the energy spectrum of one out of the five, HESS J1702-420A, up to $\simeq 300\, {\rm TeV}$ during one calendar year observation. This study concludes that ALPAQUITA will provide data enough to discuss a hot topic of VHE gamma-ray astronomy before passing the baton to ALPACA.

The ALPACA experiment is a new project aimed at wide field-of-view high-sensitivity observations of high-energy cosmic rays and cosmic gamma rays, launched between Bolivia and Japan in 2016. It is composed of an 83,000 m$^2$ air shower array and a 5,400 m$^2$ underground muon detector array, on a highland at the altitude of 4,740 m, halfway up Mount Chacaltaya on the outskirts of La Paz, Bolivia.

The calibration, alignment and commissioning of most of the ALICE (A Large Ion Collider Experiment at the CERN LHC) detectors have required a large amount of cosmic events during 2008. In particular two types of cosmic triggers have been implemented to record the atmospheric muons passing through ALICE. The first trigger, called ACORDE trigger, is performed by 60 scintillators located on the top of three sides of the large L3 magnet surrounding the central detectors, and selects atmospheric muons. The Silicon Pixel Detector (SPD) installed on the first two layers of the Inner Tracking System (ITS) gives the second trigger, called SPD trigger. This trigger selects mainly events with a single atmospheric muon crossing the SPD. Some particular events, in which the atmospheric muon interacts with the iron of the L3 magnet and creates a shower of particles crossing the SPD, are also selected. In this work the reconstruction of events with these two triggers will be presented. In particular, the performance of the ACORDE detector will be discussed by the analysis of multi-muon events. Some physical distributions are also shown.

The muon tomography technique, based on multiple Coulomb scattering of cosmic ray muons, has been proposed as a tool to detect the presence of high density objects inside closed volumes. In this paper a new and innovative method is presented to handle the density fluctuations (noise) of reconstructed images, a well known problem of this technique. The effectiveness of our method is evaluated using experimental data obtained with a muon tomography prototype located at the Legnaro National Laboratories (LNL) of the Istituto Nazionale di Fisica Nucleare (INFN). The results reported in this paper, obtained with real cosmic ray data, show that with appropriate image filtering and muon momentum classification, the muon tomography technique can detect high density materials, such as lead, albeit surrounded by light or medium density material, in short times. A comparison with algorithms published in literature is also presented.

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 m$^{2}$ with underground water Cherenkov muon detectors of total 5,400 m$^{2}$ 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 20TeV. 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 con- struction 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.