A new method using the muon lateral distribution and an underground muon detector to achieve high discrimination power against hadrons is presented. The method is designed to be applied in the Andes Large-area PArticle detector for Cosmic-ray physics and Astronomy (ALPACA) experiment in Bolivia. This new observatory in the Southern hemisphere has the goal of detecting >100 TeV γ rays in search for the origins of Galactic cosmic rays. The method uses the weighted sum of the lateral distribution of the muons detected by underground detectors to separate between air showers initiated by cosmic rays and γ rays. We evaluate the performance of the method through Monte Carlo simulations with CORSIKA and Geant4 and apply the analysis to the prototype of ALPACA, ALPAQUITA. With the application of this method in ALPAQUITA, we achieve an improvement of about 18

Observation techniques of high-energy gamma rays using air showers have remarkably progressed via the Tibet AS γ , HAWC, and LHAASO experiments. These observations have significantly contributed to gamma-ray astronomy in the northern sky’s sub-PeV region. Moreover, in the southern sky, the ALPACA experiment is underway at 4,740 m altitude on the Chacaltaya plateau in Bolivia. This experiment estimates the gamma-ray flux from the difference between the number of on-source and off-source events by real data, utilizing the gamma-ray detection efficiency calculated through Monte Carlo simulations, which in turn depends on the hadronic interaction models. Even though the number of cosmic-ray background events can be experimentally estimated, this model dependence affects the estimation of gamma-ray detection efficiency. However, previous reports have assumed that the model dependence is negligible and have not included it in the error of gamma-ray flux estimation. Using ALPAQUITA, the prototype experiment of ALPACA, we quantitatively evaluated the model dependence on hadronic interaction models for the first time. We evaluate the model dependence on hadronic interactions as less than 3.6 % in the typical gamma-ray flux estimation performed by ALPAQUITA; this is negligible compared with other uncertainties such as energy scale uncertainty in the energy range from 6 to 300 TeV, which is dominated by the Monte Carlo statistics. This upper limit of 3.6 % model dependence is expected to apply to ALPACA.

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 (1015eV − 1016eV). The experiment consists of an air shower (AS) array with a surface of 83,000m2 and an underground water Cherenkov muon detector (MD) array covering 5,400m2. The experimental site is at the Mt. Chacaltaya plateau in La Paz, Bolivia, with an altitude of 4,740m corresponding to 572g/cm2 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 (18,450m2) and underground MD (900m2), 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 10TeV and ne 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 100TeV from southern sources on the basis of the observational results of this prototype experiment.

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 4,740m altitude, a surface detector array covering 82,800m(2) with underground water Cherenkov muon detectors of total 5,400m(2) area will be constructed. Because of 2m 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.

C. Calle,a K. Hibino,b N. Hotta,c Y. Katayose,d C. Kato,e S. Kato, f K. Kawata, f W. Kihara,e Y. Ko,e H. Kojima,g R. Mayta,h P. Miranda,a H. Mitsui,i K. Munakata,e H. Nakada,i Y. Nakamura, j M. Nishizawa,k S. Ogio,h M. Ohnishi, f T. Ohura,i A. Oshima,l M. Raljevich,a H. Rivera,a T. Saito,m T. Sako∗, f T. K. Sako, f Y. Sengoku,i S. Shibata,l A. Shiomi,n M. Subieta,a N. Tajima,o W. Takano,b M. Takita, f Y. Tameda,p K. Tanaka,q R. Ticona,a H. Tsuchiya,r Y. Tsunesada,h S. Udo,b K. Yagisawa,i Y. Yokoe f aInstituto de Investigaciones Físicas, Universidad Mayor de San Andres, La Paz, La Paz 8635,

T. Asaba,a K. Hibino,b N. Hotta,c M. Kataoka,a Y. Katayose,a C. Kato,d K. Kawata∗,e H. Kojima, f g R. Mayta,h P. Miranda,i K. Munakata,d Y. Nakamura,d M. Nishizawa, j S. Ogio,h M. Ohnishi,e A. Oshima,k M. Raljevich,i H. Rivera,i T. Saito,l T. K. Sako,me T. Sasaki,a S. Shibata,k A. Shiomi,n M. Subieta,i M. Suzuki,a N. Tajima,o M. Takita,e Y. Tameda,p K. Tanaka,q R. Ticona,i H. Tsuchiya,r Y. Tsunesada,h S. Udob and M. Wakamatsua (The ALPACA Collaboration) aFaculty of Engineering, Yokohama National University, Japan bFaculty of Engineering, Kanagawa University, Japan cFaculty of Education, Utsunomiya University, Japan dDepartment of Physics, Shinshu University, Japan eInstitute for Cosmic Ray Research, The University of Tokyo, Japan f Faculty of Engineering, Aichi Institute of Technology, Japan gChubu Innovative Astronomical Observatory, Japan hGraduate School of Science, Osaka City University, Japan iInstituto de Investigaciones Físicas, Universidad Mayor de San Andrés, Bolivia jNational Institute of Informatics, Japan kCollege of Engineering, Chubu University, Japan lTokyo Metropolitan College of Industrial Technology, Japan mEscuela de Ciencias Físicas y Nanotechnología, Yachay Tech, Ecuador nCollege of Industrial Technology, Nihon University, Japan oRIKEN, Japan pFaculty of Engineering, Osaka Electro-Communication University, Japan qGraduate School of Information Sciences, Hiroshima City University, Japan rJapan Atomic Energy Agency, Japan

The Latin American Giant Observatory (LAGO) is an extended Cosmic Rays observatory composed by a network of Cherenkov Detectors (WCDs) spread over Latin America. This work will report the analysis of three years of data from three LAGO WCD located in Cerro Chacaltaya, Bolivia, at 5200 m a.s.l. Background cosmic ray rate from these detectors is checked for DAQ issues and inconsistencies, and corrected for atmospheric effects. An analysis for short transients up to the minute timescale is performed, in search for coincidence with transients observed by satellites. Sidereal and solar long term epoch data analysis are also presented.

An M6.5-class flare was observed at N12E56 of the solar surface at 16:06 UT on July 8, 2014.In association with this flare, solar neutron detectors located on two high mountains, Mt.Sierra Negra and Chacaltaya and at the space station observed enhancements in the neutral channel.The authors analysed these data and a possible scenario of enhancements produced by high-energy protons and neutrons is proposed, using the data from continuous observation of a solar surface by the ultraviolet telescope onboard the Solar Dynamical Observatory (SDO).

The Latin American Giant Observatory (LAGO) is an extended cosmic ray observatory composed by a network of water-Cherenkov detectors spanning over different sites located at significantly different altitudes (from sea level up to more than $5000$\,m a.s.l.) and latitudes across Latin America, covering a huge range of geomagnetic rigidity cut-offs and atmospheric absorption/reaction levels. This detection network is designed to measure the temporal evolution of the radiation flux at ground level with extreme detail. The LAGO project is mainly oriented to perform basic research in three branches: high energy phenomena, space weather and atmospheric radiation at ground level. LAGO is built and operated by the LAGO Collaboration, a non-centralized collaborative union of more than 30 institutions from ten countries. These are the contributions of the LAGO Collaboration to the 34th International Cosmic Ray Conference, 30 July - 6 August 2015, The Hague, The Netherlands

In the hybrid experiment on Mt.Chacaltaya, we can observe three different components of airshowers, that is, air-shower size, burst-density and high energy families (a bundle of high energy particles). Burst-density in each block of hadron calorimeters are newly recalculated in simulations in oder to compare directly to the experimental data. Energy deposits in the scintillators of the hadron calorimeters are calculated using GEANT4 for every particle, incident upon the hadron calorimeter, in the air-showers simulated using CORSIKA, and are converted into burst-density, taking into consideration the exact structure of experimental hadron calorimeter. We study correlations among three observable components in the air-showers. Correlations between air-shower size and burst-density and those between air-shower size and accompanied family energy can be explained by model calculations by adjusting primary particle composition, the former correlation is in favor of proton-primaries but the latter iron-primaries. No model can describe well observed correlations between burst-density and family energy. That is, the observed family energy accompanied by the air-showers with larger burst-density is systematically smaller than that expected in the simulated events. Effects of a fluctuation in the cross-section of hadronic interactions are studied to settle the disagreement between experimental data and simulations.

We present the results of an ongoing survey on the association between the muon flux variation at ground level (3 m above sea level) registered by the Tupi telescopes (Niteri-Brazil, 22.°9S, 43.°2W, 3 m) and the Earth-directed transient disturbances in the interplanetary medium propagating from the Sun (such as coronal mass ejections (CME), and corotating interaction regions (CIRs)). Their location inside the South Atlantic Anomaly region enables the muon telescopes to achieve a low rigidity of response to primary and secondary charged particles. The present study is primarily based on experimental events obtained by the Tupi telescopes in the period from 2010 August to 2011 December. This time period corresponds to the rising phase of solar cycle 24. The Tupi events are studied in correlation with data obtained by space-borne detectors (SOHO, ACE, GOES). Identification of interplanetary structures and associated solar activity was based on the nomenclature and definitions given by the satellite observations, including an incomplete list of possible interplanetary shocks observed by the CELIAS/MTOF Proton Monitor on the Solar and Heliospheric Observatory (SOHO) spacecraft. Among 29 experimental events reported in the present analysis, there are 15 possibly associated with the CMEs and sheaths, and 3 events with the CIRs (forward or reverse shocks); the origin of the remaining 11 events has not been determined by the satellite detectors. We compare the observed time (delayed or anticipated) of the muon excess (positive or negative) signal on Earth (the Tupi telescopes) with the trigger time of the interplanetary disturbances registered by the satellites located at Lagrange point L1 (SOHO and ACE). The temporal correlation of the observed ground-based events with solar transient events detected by spacecraft suggests a real physical connection between them. We found that the majority of observed events detected by the Tupi experiment were delayed in relation to the satellite triggers. This result agrees with theoretical expectations. Our experimental data indicate that the Tupi experiment is able to add new information and can be complementary to other techniques designed to interpret the origin of some interplanetary disturbances observed by satellites.

We compare data obtained by two secondary cosmic ray detectors with different characteristics, located at Mt Chacaltaya, Bolivia (altitude 5200m) and Niteroi, Brazil (sea level) respectively, separated by a distance of ∼2700km but both inside the so-called South Atlantic Anomaly (SAA) region, with different magnetic rigidities (cut-offs). A preliminary analysis, made on data obtained in September 2008, clearly shows some common characteristics between the two experiments, such as an increase in the intensity of charged particles from 3h after sunrise until 1h after sunset. During this period, the solar magnetic field lines overtake the Earth’s surface. We conclude that in the SAA region and at ground level secondary particles have two origins. The first is from the galactic cosmic rays and the second is from particle precipitation. Other details of these observations, like the relative composition from galactic rays and precipitation, the day/night asymmetry, as well as sunset enhancement, are reported in this paper.

The air fluorescence detector of the Pierre Auger Observatory is designed to perform calorimetric measurements of extensive air showers created by cosmic rays of above 1018eV. To correct these measurements for the effects introduced by atmospheric fluctuations, the Observatory contains a group of monitoring instruments to record atmospheric conditions across the detector site, an area exceeding 3000km2. The atmospheric data are used extensively in the reconstruction of air showers, and are particularly important for the correct determination of shower energies and the depths of shower maxima. This paper contains a summary of the molecular and aerosol conditions measured at the Pierre Auger Observatory since the start of regular operations in 2004, and includes a discussion of the impact of these measurements on air shower reconstructions. Between 1018 and 1020eV, the systematic uncertainties due to all atmospheric effects increase from 4% to 8% in measurements of shower energy, and 4gcm-2 to 8gcm-2 in measurements of the shower maximum.

Characteristics of air-shower-triggered atmospheric families detected in the hybrid experiments together with emulsion chamber and As-array at high mountains are compared with those of simulations. The analysis of families accompanied by air-showers with N(e) >= 10(7) shows that the experimental family-energy distribution favors a proton-dominant chemical composition of primary cosmic-rays but the lateral distribution favors a heavy-dominant composition. Thus no simulations can describe the overall characteristics of the data of hybrid experiments.

Atmospheric parameters, such as pressure (P), temperature (T) and density (ρ∝P/T), affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ∼10% seasonal modulation and ∼2% diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of P and ρ. The former affects the longitudinal development of air showers while the latter influences the Molière radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.

Studies of the correlations of ultra-high energy cosmic ray directions with extra-Galactic objects, of general anisotropy, of photons and neutrinos, and of other astrophysical effects, with the Pierre Auger Observatory. Contributions to the 31st ICRC, Lodz, Poland, July 2009.

On November 2, 2003 at 17:03:00 UT a solar flare, registered by the GOES satellite, was also recorded by the Neutron Monitor (NM64) of Cosmic Ray Laboratory at Mount Chacaltaya. This flare affected the local geomagnetic field (F): there were variations in the intensity of the horizontal component (H), declination component (D) and vertical component (Z). Variations on these components, estimated as 71 nT, 10 deg. and 19 nT, respectively, have been observed with the Patacamaya's Geomagnetic Observatory; as well as a net increased field (F), estimated as 66 nT, recorded by the Villa Remedios Geomagnetic Observatory. The duration of the magnetic and neutron signals was approximately 40 and 54 minutes, respectively, which shows that the flare was intense and with large emission of neutrons.

Data collected at the Pierre Auger Observatory are used to establish an upper limit on the diffuse flux of tau neutrinos in the cosmic radiation. Earth-skimming nu(tau) may interact in the Earth's crust and produce a tau lepton by means of charged-current interactions. The tau lepton may emerge from the Earth and decay in the atmosphere to produce a nearly horizontal shower with a typical signature, a persistent electromagnetic component even at very large atmospheric depths. The search procedure to select events induced by tau decays against the background of normal showers induced by cosmic rays is described. The method used to compute the exposure for a detector continuously growing with time is detailed. Systematic uncertainties in the exposure from the detector, the analysis, and the involved physics are discussed. No tau neutrino candidates have been found. For neutrinos in the energy range 2x10(17) eV <E(nu)<2x10(19) eV, assuming a diffuse spectrum of the form E(nu)(-2), data collected between 1 January 2004 and 30 April 2008 yield a 90% confidence-level upper limit of E(nu)(2)dN(nu tau)/dE(nu)<9x10(-8) GeV cm(-2) s(-1) sr(-1).