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Experiments with high angular resolution that can detect gamma rays in the 100 TeV region will help study acceleration mechanisms of gamma-ray sources with morphological characteristics. In recent years, three groups using extensive air-shower (AS) arrays have reported detecting gamma rays in the 100 TeV region from celestial bodies in the galaxy. In extensive air shower experiments, an arrival direction of a cosmic ray is determined by estimating a shape of a front surface of an air shower based on the density distribution and detection time of secondary particles. The density of secondary gamma rays of an air shower is several times that of secondary electrons and positrons in an air shower and the difference increases as the distance from the shower axis increases. Therefore, increasing the sensitivity to detect secondary gamma rays plays an important role in determining the arrival direction of the shower. Monte Carlo simulation was used to investigate the effect of secondary gamma rays on the time determination accuracy of the air shower front. When an AS array capable of measuring secondary gamma rays with 100% sensitivity was installed at an altitude of 4,740 m, the angular resolution for a 500 TeV shower was improved by about 40% compared to an array that could observe only secondary electrons and positrons. The optimum shape of the water Cherenkov detector (WCD), which is highly sensitive to gamma rays, was investigated by Monte Carlo simulation. When a water tank with a radius of 4.5 m and PMTs with a diameter of 8 inches was used, it was found that about 19 PMTs (area ratio of approximately 0.01) were suitable for detection efficiency and timing response at a water depth of 1.6 m.

We are observing extensive air showers using Tibet-III air shower array located at 4300 m above sea level. Such situation at high altitude enables us to measure the chemical composition of cosmic rays above several tens TeV by analyzing the shower profiles. A water-Cherenkov Muon Detector array (MD) was added in 2014 to measure the muon intensity of air showers and performance of particle identification was improved. We have developed a method to select proton air shower events with the energy between 30 TeV and 400 TeV by the difference of number of muons in the air shower using MD. The sensitivity of the detector for primary proton spectra was investigated by Monte Carlo simulation with both primary composition models and the interaction models. Using the number of muons measured by the MD, it was found that the protons could be selected with 90% purity. The systematic errors between these models were summarized as less than ±36% in total, indicating that the accuracy is sufficient to study the shape of the proton spectra.

We report, for the first time, the long-awaited detection of diffuse gamma rays with energies between 100 TeV and 1 PeV in the Galactic disk. Particularly, all gamma rays above 398 TeV are observed apart from known TeV gamma-ray sources and compatible with expectations from the hadronic emission scenario in which gamma rays originate from the decay of $\pi^0$'s produced through the interaction of protons with the interstellar medium in the Galaxy. This is strong evidence that cosmic rays are accelerated beyond PeV energies in our Galaxy and spread over the Galactic disk., Comment: Accepted for publication in the Physical Review Letters

We report observations of gamma-ray emissions with energies in the 100 TeV energy region from the Cygnus region in our Galaxy. Two sources are significantly detected in the directions of the Cygnus OB1 and OB2 associations. Based on their positional coincidences, we associate one with a pulsar PSR J2032+4127 and the other mainly with a pulsar wind nebula PWN G75.2+0.1 with the pulsar moving away from its original birthplace situated around the centroid of the observed gamma-ray emission. This work would stimulate further studies of particle acceleration mechanisms at these gamma-ray sources., Accepted for publication in the Physical Review Letters

We have found an interesting event registered by the solar neutron telescopes installed at high mountains in Bolivia (5250 m a.s.l.) and Mexico (4600 m a.s.l.). The event was observed November 7th of 2004 in association with a large solar flare of magnitude X2.0. Some features in our registers and in two satellites (GOES 11 and SOHO) reveal the presence of electrons and protons as possible products of neutron decay. Solar neutron decay protons (sndp) were recorded on board ISEE3 satellite in June 3rd, 1982 . On October 19th, 1989, the ground level detectors installed in Goose Bay and Deep River revealed the registration of solar neutron decay protons (sndp). Therefore this is the second example that such an evidence is registered on the Earth's surface., total 21 pages, including 13 figures submitted to Earth, Planet and Space

The extremely low flux of ultra-high energy cosmic rays (UHECR) makes their direct observation by orbital experiments practically impossible. For this reason all current and planned UHECR experiments detect cosmic rays indirectly by observing the extensive air showers (EAS) initiated by cosmic ray particles in the atmosphere. The world largest statistics of the ultra-high energy EAS events is recorded by the networks of surface stations. In this paper we consider a novel approach for reconstruction of the arrival direction of the primary particle based on the deep convolutional neural network. The latter is using raw time-resolved signals of the set of the adjacent trigger stations as an input. The Telescope Array (TA) Surface Detector (SD) is an array of 507 stations, each containing two layers plastic scintillator with an area of $3$ m$^2$. The training of the model is performed with the Monte-Carlo dataset. It is shown that within the Monte-Carlo simulations, the new approach yields better resolution than the traditional reconstruction method based on the fitting of the EAS front. The details of the network architecture and its optimization for this particular task are discussed., Accepted by Machine Learning: Science and Technology

On 2011 March 7, the Solar Neutron Telescope located at Mt. Sierra Negra, Mexico (4600 m) observed enhancements of the counting rate from 19:57 to 20:04 UT with statistical significance 6.8σ and from 20:36 to 21:03 UT with 5.8σ. One plausible physical explanation for the observation enhancements is that they were produced by solar gamma-rays. The intensities were estimated to be (0.16 ± 0.03) photons cm−2 s−1 for the first flare and (0.22 ± 0.04) photons cm−2 s−1 for the second one at the top of the atmosphere. As far as we know, this is the first report on the detection of solar gamma-rays with a ground-based detector. In association with these events, the solar neutron detector Space Environment Data Acquisition Equipment on board the International Space Station registered two solar neutrons with statistical significances of 7.3σ and 6.6σ. The Large Area Telescope on board the Fermi observatory also observed high-energy gamma-rays from this flare with a statistical significance of 6.7σ. In this paper we propose a unified model to explain the production mechanism of high-energy gamma-rays and neutrons in association with this flare.

Motivated by the detection of a significant dipole structure in the arrival directions of ultrahigh-energy cosmic rays above 8 EeV reported by the Pierre Auger Observatory (Auger), we search for a large-scale anisotropy using data collected with the surface detector array of the Telescope Array Experiment (TA). With 11 years of TA data, a dipole structure in a projection of the right ascension is fitted with an amplitude of 3.3+- 1.9% and a phase of 131 +- 33 degrees. The corresponding 99% confidence-level upper limit on the amplitude is 7.3%. At the current level of statistics, the fitted result is compatible with both an isotropic distribution and the dipole structure reported by Auger., Comment: 6 pages, 3 figures, 1 table, Proofed title. Added journal reference and DOI

Machine learning is a powerful tool used in many different areas, from image processing to space navigation and high-energy physics. In this paper we present a configuration of different artificial intelligent tools aimed at the extraction of features from data registered in the SciBar Cosmic Ray Telescope (SciCRT). The SciCRT is an array of plastic scintillator bars that work nearly independently as particle detectors. When a particle crosses inside the telescope, scintillation photons are emitted by the plastics. The intensity of photons is directly proportional to the energy deposited in each bar. Taking advantage of the construction of the telescope, the small transverse area of the scintillator bars, it is possible to do particle tracking and analysis. The main purpose of SciCRT is the detection of solar neutrons originated in the violent phenomena taking place at the surface of the Sun. Nonetheless, the SciCRT is capable of detecting different kinds of secondary particles produced by the interactions of primary cosmic rays with the atmospheric nuclei. For this reason, the task of signal classification is essential. Our final goal will be the classification of detected cosmic ray particles, as well as, the unfolding of the neutron energy spectrum and the estimation of the angular distribution. To achieve this our methodology relies of pattern recognition, artificial neural networks, k-means clustering and k-Nearest Neighbors. In addition, our paper presents a Monte Carlo simulation of the SciCRT for the training and evaluation of the machine learning algorithms.

We propose a new energy estimator to determine the energies of gamma-ray induced air showers based on the lateral distribution of extensive air showers in the energy range between 10 TeV and 1000 TeV. We carry out a detailed Monte Carlo simulation assuming the Tibet air shower array located at an altitude of 4,300 m above sea level. We define S50, which denotes the particle density at 50 m from the air shower axis, as a new energy estimator. Using S50, the energy resolution is estimated to be approximately 16 % at 100 TeV in the range of the zenith angle 𝜃 < 20∘. We find S50 giving a better energy resolution than 27 % for the air shower size (N e) and 30 % for the sum of detected particles ( $\sum \rho $ ), which have been used so far, at 100 TeV. We also compare the reconstructed age distributions of gamma-ray induced air showers and hadronic cosmic-ray induced air showers. The age parameter may help to discriminate between primary gamma rays and hadronic cosmic rays.

The Tibet air-shower (AS) array has been in operation since 1990 at the altitude of 4,300 m in Tibet, China, to observe cosmic rays and gamma rays above TeV energies. The muon detector (MD) array has been in operation successfully since 2014 to improve the sensitivity of the Tibet AS array toward gamma rays above 10 TeV. The MD array records the charge and timing infor- mation of the water cells in synchronization with event trigger signals from the AS array. We can discriminate gamma rays from cosmic-ray nuclei based on the number of muons in air showers measured by the MD array, and thus suppress over 99.9% of background cosmic-ray events above 100 TeV. G106.3+2.7 is a supernova remnant, with the so-called“ Boomerang ”pulsar wind neb- ula located at its northeast edge. Above TeV energies G106.3+2.7 has been detected by Milagro and VERITAS. In this presentation we report on the observation of gamma-ray emission above 10 TeV from G106.3+2.7, using the data taken by the Tibet AS array and the MD array.

Cosmic-ray experiments including ground-based air-shower arrays as well as underground muon telescopes have reported the existence of anisotropy in the arrival directions of galactic cosmic rays. The origin of the anisotropy, however, has not been fully understood yet. At sub-TeV energies, the anisotropy does not exhibit a 22-year cycle variation expected from the reverse of the solar dipole magnetic field, although the amplitude of the anisotropy becomes attenuated by solar modulation effects. At TeV energies, there is not an established model for two distinct large-scale structures reported by a lot of experiments: a deficit region called the “loss-cone” and an excess region called the “tail-in”. Above ∼100TeV, it has been pointed out that the amplitude and the phase of the anisotropy begin to change dramatically compared with those at TeV energies. The anisotropy reflects how cosmic rays propagate through the magnetic field in the heliosphere and the surrounding interstellar medium. In this presentation we study the influence of the heliosphere on the anisotropy by tracking particle trajectories in a heliosphere reconstructed from MHD simulations. We also discuss the anisotropy outside the heliosphere that can be derived from the experimental data obtained by the Tibet AS array.

Ion-induced nucleation by cosmic rays influenced by solar modulation is of interest, and several studies with radioactive sources or accelerator beams have been performed. We focused on ionization with high-linear energy transfer (LET) particles, such as protons, neutrons, and ions, in secondary cosmic rays and the ion density of the secondary cosmic rays near the ground using the excel-based program for calculating atmospheric cosmic-ray spectrum (EXPACS). According to the calculation, not only muons but also protons and neutrons leave substantial traces of solar modulation at an altitude of 3 km from the ground. To verify the ion-induced nucleation by these secondary high-LET cosmic rays, a chamber experiment was conducted at the accelerator facility HIMAC. Using a chamber with a capacity of 75 L, experiments were conducted by irradiating protons and nitrogen ion beams with a constant energy of 180 MeV/u with varying intensity. The experimental results confirm that the ion density and aerosol density increased as the beam intensity increased. The aerosol density was found to be proportional to the ion density, but irrelevant to the ionization density. It was concluded that the ion-induced nucleation by high-LET secondary cosmic rays, such as protons and neutrons, provides no evidence of enhancement owing to ionization density and cannot account for the claimed variation of cloud formation due to the solar modulation.

We present an upper limit on the flux of ultra-high-energy down-going neutrinos for $E > 10^{18}\ \mbox{eV}$ derived with the nine years of data collected by the Telescope Array surface detector (05-11-2008 -- 05-10-2017). The method is based on the multivariate analysis technique, so-called Boosted Decision Trees (BDT). Proton-neutrino classifier is built upon 16 observables related to both the properties of the shower front and the lateral distribution function., 10 pages, 4 figures, accepted to JETP

This paper presents a simulation/experimental technique used in the design of optimum performance read-out electronics for a new cosmic ray telescope composed of scintillator bars. This new detector, called SciBar Cosmic Ray Telescope (SciCRT), is installed on top of Sierra Negra volcano in Mexico, operating at an atmospheric depth of 575 g cm−2. The severe atmospheric conditions and high background rate of the place currently limit the performance of the detector, therefore the requirements of our design are low power consumption and high throughput rate. The simulation developed considers the interaction of high energy cosmic ray muons with the scintillator bar, generation and propagation of photons inside a wavelength shifting fiber (WLS) fiber and the detection by a multi-anode photomultiplier (MAPMT). To produce realistic signals coming from the interaction of particles, our method relies on the extraction of different parameters throughout experiment to include them in the simulation. In addition, the paper presents a muon cosmic ray experiment designed to validate the results of the simulation and test the performance of the new electronics.

We report on a measurement of the cosmic ray composition by the Telescope Array Low-Energy Extension (TALE) air fluorescence detector (FD). By making use of the Cherenkov light signal in addition to air fluorescence light from cosmic ray (CR) induced extensive air showers, the TALE FD can measure the properties of the cosmic rays with energies as low as $\sim 2$ PeV and exceeding 1 EeV. In this paper, we present results on the measurement of $X_{\rm max}$ distributions of showers observed over this energy range. Data collected over a period of $\sim 4$ years was analyzed for this study. The resulting $X_{\rm max}$ distributions are compared to the Monte Carlo (MC) simulated data distributions for primary cosmic rays with varying composition and a 4-component fit is performed. The comparison and fit are performed for energy bins, of width 0.1 or 0.2 in $\log_{10} (E/{\rm eV})$, spanning the full range of the measured energies. We also examine the mean $X_{\rm max}$ value as a function of energy for cosmic rays with energies greater than $10^{15.8}$ eV. Below $10^{17.3}$ eV, the slope of the mean $X_{\rm max}$ as a function of energy (the elongation rate) for the data is significantly smaller than that of all elements in the models, indicating that the composition is becoming heavier with energy in this energy range. This is consistent with a rigidity-dependent cutoff of events from galactic sources. Finally, an increase in the $X_{\rm max}$ elongation rate is observed at energies just above $10^{17}$ eV indicating another change in the cosmic rays composition., 20 pages, 22 figures, accepted for publication in ApJ

International audience; The LHCf experiment is an LHC experiment dedicated to measure the production spectra of forward neutral particles, photons, \(\pi ^{0}\)s and neutrons. The obtained results are very useful to test hadronic interaction models which are used in MC simulations for cosmic-ray air shower developments. The LHCf had an operation in 2015 with p–p collisions at \(\sqrt{s} \) = 13 TeV, which corresponds to the collision energy of 0.9 × 10^17 eV in the laboratory frame. We discuss the results of the inclusive energy spectra for forward photons obtained at p–p, \(\sqrt{s} \) = 13 TeV data as well as \(\pi ^{0}\) results taken at p–p, \(\sqrt{s} \) = 7 TeV. In addition we introduce future prospects of LHCf analyses and activities.

The Relativistic Heavy Ion Collider forward (RHICf) experiment has measured neutral particles produced in the very forward direction in the √s=510 GeV proton-proton collisions at RHIC in June 2017. The production cross sections of these particles are crucial to understand the hadronic interaction relevant to the air shower development at the cosmic-ray equivalent energy of 1.4×10$^{14}$ eV, just below the energy of the knee. Together with the data at LHC, accelerator data can cover the interaction in the cosmic-ray energy of 10$^{14}$ eV to 10$^{17}$ eV. In addition, RHICf is able to improve the former measurements of single-spin asymmetry in the polarized proton- proton collisions that is sensitive to the fundamental process of the meson exchange. Common data taking with the STAR experiment will shed light on the unexplored low mass diffraction process.

To understand the forward particle production in hadronic collisions, the Large Hadron Collider forward (LHCf) experiment has performed measurements at the LHC under various collision condition. The data of particle production at the highest accelerator energy are expected to im- prove the interpretation of the cosmic-ray air shower observation data, and hence to improve the knowledge of the cosmic-ray origin. Brief overview of the LHCf results obtained from the proton-proton collisions at √s=0.9, 2.76, 7 and 13 TeV and results from the proton-lead collisions at √s=5.02 TeV are presented. To explore the lower collision energy, √s=510 GeV, preparation of a new experiment the Relativistic Heavy Ion Collider forward (RHICf) is on going. Physics motivations and status of the RHICf are also presented.

The SciBar Cosmic ray telescope (SciCRT) is installed on the top of the Sierra Negra volcano with the main goal of observing solar neutrons to investigate the ion acceleration process during solar flares. Using scintillator bars as a medium to stop energetic particles, the SciCRT is capable of recording both energy deposited on the bars and direction of the incoming particles with high resolution. The original DAQ system was used in neutrino oscillation experiment (low event rate), therefore operation of the electronics on cosmic ray experiment is limited. To improve the SciCRT performance as a solar neutron telescope, development of custom made DAQ electronics is essential. Our first step onto this task was the design and construction of a new fast readout back-end board using SiTCP. The installation of this new system on Sierra Negra and its further improvement on the data acquisition for the detector will be analyzed on separate paper on this conference. The development of new front end electronics is the next stage of the upgrading process. To achieve this goal, we are developing new electronics applying the time over threshold (ToT) technique, using a FPGA to process the signal from one 64 channel multi anode photomutiplier tube (MAPMT). In this paper we will present the details of this new system and several tests performed to guarantee its proper operation to detect solar neutrons.

The SciBar Cosmic Ray Telescope (SciCRT) is aimed to help elucidate the acceleration mechanism of high-energy ions that may produce neutrons at the Sun. It is a fully active scintillator tracker which consists of 14,848 plastic scintillator bars, originally constructed for accelerator neutrino oscillation experiments. The SciCRT; it has a huge detector volume compared with conventional Solar Neutron Telescopes (SNTs), e.g. 15 times larger than Mexico SNT. Furthermore, the SciCRT can measure the energy deposition of each particle as neutron ADC data which have not been registered before. Neutron ADC data provide us with a precise measurement of energies deposited at the detector. The SciCRT was deployed at the summit of Mt. Sierra Negra (4,600 m) and began to acquire data in September 2013. Then we partially upgraded the DAQ system developed originally for an accelerator experiment, as the readout rate of the DAQ system was significantly limited for our experiment. This paper highlights sensitivity numerical studies of solar neutrons that the SciCRT is able to register. At first, we focus in the accuracy to determine the spectrum power-law index, assuming an instantaneous emission of solar neutrons. This is required to determine the power-law index within an error of ±1.0 in order to discuss the efficiency of the acceleration. Then in the case of the fixed power-law index, we discuss the capability of discriminating three different lengths of emission times: 0 min, 5 min, and 8 min. Finally we evaluate whether it is possible to discriminate a different combination of these two parameters simultaneously. Thus, we show that data from the SciCRT will unlock the degeneracy problem amid the emission time and the energy spectrum of solar neutrons.

At the 33rd ICRC, we reported the possible detection of solar gamma rays by a ground level detector and later re-examined this event. On March 7, 2011, the solar neutron telescope (SNT) located at Mt. Sierra Negra, Mexico (4,600 m) observed enhancements of the counting rate from 19:49 to 20:02 UT and from 20:50 to 21:01 UT. The statistical significance was 9.7sigma and 8.5sigma, respectively. This paper discusses the possibility of using this mountain detector to detect solar gamma rays. In association with this event, the solar neutron detector SEDA-FIB onboard the International Space Station has also detected solar neutrons with a statistical significance of 7.5sigma. The FERMI-LAT detector also observed high-energy gamma rays from this flare with a statistical significance of 6.7sigma. We thus attempted to make a unified model to explain this data. In this paper, we report on another candidate for solar gamma rays detected on September 25th, 2011 by the SNT located in Tibet (4,300 m) from 04:37 to 04:47 UT with a statistical significance of 8.0sigma (by the Li-Ma method)., 15 pages

The Large Hadron Collider forward (LHCf) experiment was motivated to understand the hadronic interaction processes relevant to cosmic-ray air shower development. We have developed radiation-hard detectors with the use of Gd2SiO5 (GSO) scintillators for proton-proton ?s = 13 TeV collisions. Calibration of such detectors for photon measurement has been completed at the CERN SPS T2-H4 line in 2015 using electron beams of 100-250 GeV and muon beams of 150-250 GeV . After the channel-by-channel absolute energy calibration, the energy resolution of the calorimeters is confirmed to be better than 3% for electrons with energy above 100 GeV . The position dependence of the energy scale of the calorimeters was reduced to the level of 1% after the corrections for scintillator nonuniformity and the shower leakage effect. The position resolution of the new shower imaging detector, a GSO-bar hodoscope interleaved in the calorimeter, was 100 ?m for 200 GeV electrons. The experimental results are well explained by Monte Carlo simulations. We have confirmed that the new detectors meet the requirement of the LHCf experiment at ?s = 13 TeV. © 2017 IOP Publishing Ltd and Sissa Medialab srl.

We have upgraded the new Tibet ASgamma experiment in China since 2014 to measure the chemical composition of cosmic rays around the knee. This hybrid experiment consist of an air-shower-core detector array (YAC-II) to detect high energy electromagnetic component, the Tibet air-shower array (Tibet-III) and a large underground water-Cherenkov muon-detector array (MD). We have carried out a detailed air-shower Monte Carlo (MC) simulation to study the performance of the hybrid detectors by using CORSIKA (version 7.5000), which includes EPOS-LHC, QGSJETII-04, SIBYLL2.1 and SIBYLL2.3 hadronic interaction models. The preliminary results of the interaction model checking above 50 TeV energy region are reported in this paper, and the primary proton and helium spectra in the energy range 50 TeV to 1015 eV was derived from YAC-I data and is smoothly connected with direct observation data at lower energies and also with our previously reported works at higher energies within statistical errors. The knee of the (P+He) spectra is located around 400 TeV. The interaction model dependence in deriving the primary (P+He) spectra is found to be small (less than 25% in absolute intensity, 10% in position of the knee), and the composition model dependence is less than 10% in absolute intensity.

We analyze the temporal variation of the solar diurnal anisotropy of the multi-TeV cosmic-ray intensity observed with the Tibet air shower array from 2000 to 2009, covering the maximum and minimum of the 23rd solar cycle. We comfirm that a remarkable additional anisotropy component is superposed on the Compton-Getting anisotropy at 4.0 TeV, while its amplitude decreases at higher energy regions. In constrast to the additional anisotropy reported by the Matsushiro experiment at 0.6 TeV, we find the residual component measured by Tibet at multi-TeV energies is consistent with being stable, with a fairly constant amplitude of 0.041% ± 0.003% and a phase at around 07.17 ± 00.16 local solar time at 4.0 TeV. This suggests the additional anisotropy observed by the Tibet experiment could result from mechanisms unrelated to solar activities.

The Large Hadron Collider forward and the Relativistic Heavy Ion Collider forward experiments measured forward particles produced in high-energy hadron collisions at the LHC and RHIC. Using compact calorimeters neutral particles produced in pseudorapidities η >8.4 and η >6.0 are observed by the respective experiments. Because the collision energies ranging from 0.51 TeV to 13 TeV correspond to the cosmic-ray equivalent energies of 1014 to 1017 eV, the measurements are important to understand the hadronic interaction relevant to extensive air shower measurements. This paper reviews recent results of LHCf and initial performance of RHICf that took data in the 2017 RHIC operation.

We report on the first results of a unique in-situ experimental cross-calibration effort of the surface detector of the Pierre Auger Observatory and of the Telescope Array experiment (Auger@TA). In the first phase of Auger@TA, we performed surface detector station-to-station comparisons for a collection of extensive air showers landing near the experimental setup and detected by Telescope Array. Beyond the deduced cross-calibration curve between the Water-Cherenkov-based Auger and Scintillator-based TA Surface Detector stations, we also investigate the consistency of their response for individual reconstructed showers. The dataset is currently too small to draw firm conclusions as-of-yet. Hence, phase I data taking will continue even as we gear up for the deployment of an Auger micro-array within Telescope Array as part of Phase II of this work.

We study the energy determination of the gamma-ray induced air shower and gamma/hadron separation using the lateral distribution of extensive air shower in the energy range between 10 TeV and 1000 TeV. For this purpose, we carry out a detailed MC simulation assuming the Tibet air shower array located in Tibet, at an altitude of 4,300 m above sea level. In this paper, we define S30, which is the particle density at 30 m from the air shower axis, as a new energy estimator. Using the S30, the energy resolutions are estimated to be approximately 40% at 10 TeV and 15% at 100 TeV in the rage of the zenith angle q < 20 ◦ . We also compare the reconstructed age distribution between the gamma-ray induced air shower and the hadronic cosmic-ray air shower. The age parameter may help to discriminate between the primary gamma rays and the hadronic cosmic rays independent of the muon information.

The LHCf experiment, optimized for the study of forward physics at LHC, completes its main physics program in this year 2015, with the proton-proton collisions at the energy of 13 TeV. LHCf gives important results on the study of neutral particles at extreme pseudo-rapidity, both for proton-proton and for proton-ion interactions. These results are an important reference for tuning the models of the hadronic interaction currently used for the simulation of the atmospheric showers induced by very high energy cosmic rays. The results of this analysis and the future perspective are presented in this paper.

The observation of the extensive air showers has been carried out since 1990 by Tibet air-shower array to study the origin of the cosmic-rays. In order to investigate the chemical composition around the knee, air-shower core detector was used in two experimental phases aiming to separate light primary elements (proton and helium). In a first phase experiment made in 1996-1999, primary proton and helium spectra were measured using a hybrid detector consisted of Tibet II air-shower array, emulsion chambers, and burst detectors. The result indicated that the fraction of light elements among the all particle spectrum is less than 30%. We performed the second phase experiment in 2002-2005 to measure proton + helium together to confirm the previous result with higher statistics by improving the detection efficiency for the air-shower cores. The P + He spectrum was obtained in a good agreement with previous result by several times higher statistics. The flux of the light elements, together with the all-particle energy spectrum, indicates the dominance of nuclei heavier than helium in the energy range around the knee. We also present the outline of the next phase experiment, which is to measure the heavy elements around the knee, using low threshold air-shower core detector named YAC. (C) 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.

LHCf is a high-energy physics experiment designed to study the forward production of neutral particles in proton–proton collisions at the LHC. The set-up consists of two small calorimetric systems symmetrically placed 140 m away on both the sides of the ATLAS interaction point. Results from the experiment will provide valuable information to the calibration of the nuclear interaction models used in the Monte Carlo codes for air-shower simulations, which are of great importance for present and future ground-based cosmic-ray experiments. In particular, since LHCf will start taking data in the first phase of operation of the LHC (during the beam commissioning phase at 5 + 5 TeV energy) and will complete its data taking at the beginning of the 7 + 7 TeV runs (laboratory equivalent collision energy 10 17 eV ), it will span an energy range up to the region between the “knee” and the GZK cut-off of the cosmic-ray spectrum.

The LHCf experiment is the smallest of the six experiments installed at the Large Hadron Collider (LHC). While the general purpose detectors have been mainly designed to answer the open questions of Elementary Particle Physics, LHCf has been designed as a fully devoted Astroparticle experiment at the LHC. Indeed, thanks to the excellent performances of its double arm calorimeters, LHCf will be able to measure the flux of neutral particles produced in p-p collisions at LHC in the very forward region, thus providing an invaluable help in the calibration of air-shower Monte Carlo codes currently used for modeling cosmic rays interactions in the Earth atmosphere. Depending on the LHC machine schedule, LHCf will take data in an energy range from 900 GeV up to 14 TeV in the centre of mass system (equivalent to 10 17 eV in the laboratory frame), thus covering one of the most interesting and debated region of the Cosmic Ray spectrum, the region around and beyond the “knee”.

A new gamma ray observation project with balloon borne emulsion chambers is presented. A new technique based on the accelerator emulsion experiments was implemented for studying high energy stellar objects with cosmic gamma rays. This paper provides the aim and concept of this project as well as some results of test experiments.

The Sun provides unique opportunities to study particle acceleration mechanisms using data from detectors placed on the Earth’s surface and on board spacecrafts. Particles may gain high energies by several physical mechanisms. Differentiating between these possibilities is a fundamental problem of cosmic ray physics. Energetic neutrons provide us with information that keeps the signatures of the acceleration site. A summary of some representative solar neutron events observed on the Earth’s surface, including associated X and γ-ray observations from spacecrafts is presented. We discuss evidence of acceleration of particles by the Sun to energies up to several tens of GeV. In addition, a recent solar neutron event that occurred on September 7th 2005 and detected by several observatories at Earth is analyzed in detail.

Relativistic neutrons were observed by the neutron monitors at Mt. Chacaltaya and Mexico City and by the solar neutron telescopes at Chacaltaya and Mt. Sierra Negra in association with an X17.0 flare on 2005 September 7. The neutron signal continued for more than 20 min with high statistical significance. Intense emissions of γ -rays were also registered by INTEGRAL , and during the decay phase by RHESSI . We analyzed these data using the solar-flare magnetic-loop transport and interaction model of Hua et al. [Hua, X.-M., Kozlovsky, B., Lingenfelter, R.E. et al. Angular and energy-dependent neutron emission from solar flare magnetic loops, Astrophys. J. Suppl. Ser. 140, 563–579, 2002], and found that the model could successfully fit the data with intermediate values of loop magnetic convergence and pitch-angle scattering parameters. These results indicate that solar neutrons were produced at the same time as the γ -ray line emission and that ions were continuously accelerated at the emission site.

We are planning to build a large water-Cherenkov-type muon detector array around the Tibet air shower array for Gamma-ray astronomy in the 100 TeV Region. In this paper, we describe the design of the Tibet MD array and details of the Monte Carlo simulation to demonstrate the sensitivity of the Tibet AS+MD array.

The Tibet air shower array with effective area 37,000 m 2 located at 4300m in altitude, in Tibet, China, is sensitive to celestial gamma rays with energies above a few TeV. We have a plan to add a large underground muon detector array to it in order to discriminate cosmic gamma rays from cosmic-ray hadrons and to increase its sensitivity by approximately one order of magnitude to cosmic gamma rays in the 100 TeV energy region. The overview of the plan will be briefly described.

We searched for steady 100 TeV gamma-ray point sources from −10° to +70° in declination based on six year data obtained from Nov. 1999 to Nov. 2005 by the Tibet air shower array. No new source was found and no significant excess of events could be detected from known TeV sources. We set flux upper limits above 100 TeV on several nearby objects located inside Our Galaxy. All of them are slightly higher than extrapolation from lower energies by a factor of 1 to 20. Our new project named Tibet MD will improve our sensitivity by a factor of ∼10 in this energy region. We would discover ∼10 new sources and be able to measure cutoff energy of known and unknown sources, which might lead to identification of the origin of cosmic rays.

In association with the large solar flare of April 15, 2001, the Chacaltaya neutron monitor observed a 3.6σ enhancement of the counting rate between 13:51 and 14:15 UT. Since the enhancement was observed beginning 11 min before the GLE, solar neutrons must be involved in this enhancement. The integral energy spectrum of solar neutrons can be expressed by a simple power law in energy with the index γ = - 3.0 ± 1.0 . On the other hand, an integral energy spectrum of solar protons has been obtained in the energy range between 650 MeV and 12 GeV. The spectrum can also be expressed by a power law with the power index γ = - 2.75 ± 0.15 . The flux of solar protons observed at Chacaltaya (at ⩾12 GeV) was already one order less than the flux of the galactic cosmic rays. It may be the first simultaneous observation of the energy spectra of both high-energy protons and neutrons. Comparing the Yohkoh soft X-ray telescope images with the observed particle time profiles, an interesting picture of the particle acceleration mechanism has been deduced.

We report on the spectral index of cosmic rays around 10 TeV energy region obtained by observation of the Compton-Getting anisotropy due to the terrestrial orbital motion around the Sun with the Tibet III air shower array during the period from 1999 to 2005. The spectral index has turned out to be 2.99 ± 0.54 , which is consistent with 2.74 by the direct energy spectrum measurement. This method is a new approach to measure the spectral index and is complementary to the conventional energy spectrum measurement.

A new solar neutron telescope has been constructed at Yangbajing, Tibet (600 g/cm(2)) and has been successfully operated for 8 years. During this time several interesting events were observed in coincidence with large solar flares. In this paper the authors discuss a directional count rate enhancement 1998 November 28 as to whether it is related to solar phenomena or not. We use this event to evaluate the sensitivity of the solar neutron telescope and discuss the detection limit for solar neutrons and high energy solar protons of this detector. (C) 2007 Elsevier B.V. All rights reserved.

We have successfully detected solar neutrons at ground level in association with the X17.0 solar flare that occurred on 2005 September 7. Observations were made with the solar neutron telescopes and neutron monitors located in Bolivia and Mexico. In this flare, large fluxes of hard X-rays and γ-rays were observed by the GEOTAIL and the INTEGRAL satellites. The INTEGRAL observations include the 4.4 MeV line γ-rays of 12 C. The data suggest that solar neutrons were produced at the same time as these hard electromagnetic radiations. We have however found an apparent discrepancy between the observed and the expected time profiles. This fact suggests a possible extended neutron emission.

The Large Hadron Collider forward (LHCf) experiment is designed to use the LHC to verify the hadronic-interaction models used in cosmic-ray physics. Forward baryon production is one of the crucial points to understand the development of cosmic-ray showers. We report the neutron-energy spectra for LHC $\sqrt{s}$ = 7 TeV proton--proton collisions with the pseudo-rapidity $\eta$ ranging from 8.81 to 8.99, from 8.99 to 9.22, and from 10.76 to infinity. The measured energy spectra obtained from the two independent calorimeters of Arm1 and Arm2 show the same characteristic feature before unfolding the difference in the detector responses. We unfolded the measured spectra by using the multidimensional unfolding method based on Bayesian theory, and the unfolded spectra were compared with current hadronic-interaction models. The QGSJET II-03 model predicts a high neutron production rate at the highest pseudo-rapidity range similar to our results and the DPMJET 3.04 model describes our results well at the lower pseudo-rapidity ranges. However no model perfectly explains the experimental results in the whole pseudo-rapidity range. The experimental data indicate the most abundant neutron production rate relative to the photon production, which does not agree with predictions of the models., Comment: 10pages, 6 figures

Strong signals of neutral emissions were detected in association with a solar flare that occurred on 2005 September 7. They were produced by both relativistic ions and electrons. In particular, relativistic neutrons were observed with the solar neutron telescopes (SNTs) located at Mount Chacaltaya in Bolivia and Mount Sierra Negra in Mexico and with neutron monitors (NMs) at Chacaltaya and Mexico City with high statistical significances. At the same time, hard X-rays and γ-rays, which were predominantly emitted by high-energy electrons, were detected by the Geotail and the INTEGRAL satellites. We found that a model of the impulsive neutron emission at the time of the X-ray/γ-ray peak can explain the main peaks of all the detected neutron signals, but failed to explain the long tailed decaying phase. An alternative model, in which the neutron emission follows the X-ray/γ-ray profile, also failed to explain the long tail. These results indicate that the acceleration of ions began at the same time as the electrons but that ions were continuously accelerated or trapped longer than the electrons in the emission site. We also demonstrate that the neutron data observed by multienergy channels of SNTs put constraints on the neutron spectrum.

The Sun was intensely active from late October to the beginning of November 2003. A series of 11 X class solar flares occurred in NOAA regions 484, 486 and 488. Unique among this series of flares were those occurring on November 2 and 4 in which solar neutrons were observed by the ground based neutron monitors located at Mt. Chacaltaya, Bolivia and Haleakala, Hawaii, respectively. In these flares, intense emission of hard X-rays and γ-rays have been observed by the satellites. It seems that production of solar neutrons coincided with the production of the hard electromagnetic radiations of these two flares.

We have succeeded in operating the 64 m 2 solar neutron detector based on 24 W power consumption. The detector has been operated at the Mount Norikura Cosmic Ray Observatory (2770 m ) with the small amount of power delivered by solar cell arrays and windmills, without generator service, throughout severe winter of 2003–2004. The results of our experiences are described.

The LHC-forward (LHCf) experiment, situated at the LHC accelerator, has measured neutral particles production in a very forward region (pseudo-rapidity > 8.4) in proton-proton and proton-lead collisions. The main purpose of the LHCf experiment is to test hadronic interaction models used in cosmic rays experiments to imulate cosmic rays induced air-showers in Earth’s atmosphere.The experiment is composed of two independent detectors located at 140m from the ATLAS interaction point (IP1) on opposite sides ; each detector is composed of two sampling calorimeters.Latest physics results from p-p and p-Pb collisions (at √s = 7 TeV and 5.02 TeV respectively) will be discussed in this paper ; in particular, the inclusive energy spectra of neutrons in p-p collisions and the transverse momentum spectra of neutral pions for different pseudo-rapidity ranges in p-Pb collisions will be shown.

A neutron beam dump experiment has been carried out using the accelerator beam at RCNP, Osaka University. Neutrons with energies Tn=100– 400 MeV were allowed to bombard a carbon target (density 1.8 g / cm 3 ) which had a thickness varying from 0 to 300 cm , and the attenuation of the neutrons was measured in the range from 0 to 540 g / cm 2 . The experimental data were well reproduced by the Monte Carlo calculation by the Shibata model. Using these results, the attenuation of neutrons in the Earth's atmosphere was obtained by means of a simulation. The results are useful not only for cosmic ray experiments but also for radiation protection experiments since the target does not contain hydrogen.

The neutron monitor developed by Simpson (Phys. Rev. 73 (1948) 1389) has been widely used to measure the intensity of cosmic rays. However, the detection efficiency of the neutron monitor has never been calibrated using an accelerator beam. This paper gives the first results of measurements of the detection efficiency of the neutron monitor using the accelerator beam at RCNP, Osaka University. The experimental data reproduce both the early prediction by Hatton and the recent calculation by Clem surprisingly well.

A new type solar neutron detector has been developed and a few have been installed on several high mountains around the world. Till now, seven solar neutron detectors have been operated for the observation of solar neutrons in association with solar flares. For the purpose of calibrating the detection efficiency of this new type of solar neutron detector, we carried out an accelerator experiment at the Research Center for Nuclear Physics of Osaka University between February 1996 and June 1999. In this paper, we report the detection efficiency obtained by the accelerator experiment and the results are compared with Monte Carlo simulations.