Performances and long-term stability of the LHAASO-KM2A prototype array

A prototype array for the LHAASO-KM2A, which consists of 42 detector units and fully overlaps the ARGO-YBJ experiment, was set up at the Yangbajing cosmic ray observatory and has been in stable operation since Octoter 2010. The resulting performances of the KM2A electromagnetic particle detector prototypes fully meet the design requirements. Through hybrid observation of cosmic ray showers with the ARGO-YBJ experiment, the performances and long-term stability of the prototype array are tested and the results are consistent with expectation. The cosmic ray moon shadow observed by the prototype array is also presented.     

A future project at tibet: the large high altitude air shower observatory (LHAASO)

Gamma ray source detection above 30 TeV is an encouraging approach for finding galactic cosmic ray sources. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulation for various types of sources above 100 GeV. In order to target those goals, a large air shower particle detector array of 1 km~2 (the LHAASO project) at 4300 m a.s.l, is proposed. By adding two MagicII-type telescopes in the array as proposed, LHAASO will be enhanced in source morphologic investigation power. The proposed array will be utilized also for energy spectrum measurement for individual cosmic ray species above 30 TeV. By re-configuring the wide field of view telescopes into fluorescence light detector array, the aperture of the detector array can be enlarged to cover an energy region above 100 PeV where the second knee is located. Cosmic ray spectrum and composition will be measured in order to transfer an energy scale to ultra high energy cosmic ray experiments.     

A future project at tibet： the large high altitude air shower observatory （LHAASO）

Gamma ray source detection above 30 TeV is an encouraging approach for finding galactic cosmic ray sources. All sky survey for gamma ray sources using wide field of view detector is essential for population accumulation for various types of sources above 100 GeV. In order to target those goals, a large air shower particle detector array of 1 km^2 （the LHAASO project） at 4300 m a.s.l, is proposed, By adding two MagicⅡ- type telescopes in the array as proposed, LHAASO will be enhanced in source morphologic investigation power. The proposed array will be utilized also for energy spectrum measurement for individual cosmic ray species above 30 TeV. By re-configuring the wide field of view telescopes into fluorescence light detector array, the aperture of the detector array can be enlarged to cover an energy region above 100 PeV where the second knee is located. Cosmic ray spectrum and composition will be measured in order to transfer an energy scale to ultra high energy cosmic ray experiments.     

近地雷暴电场与羊八井地面宇宙线关联的模拟研究

雷暴期间地面宇宙线强度变化的研究对理解大气电场加速宇宙线次级带电粒子的物理机理具有重要意义. 分析西藏羊八井ARGO实验中2012年大气电场的数据后发现, 近地雷暴电场的强度可达1000 V/cm甚至更高. 用Monte Carlo方法模拟研究了近地雷暴电场与羊八井地面宇宙线强度的关联. 当雷暴电场强度(取1500 V/cm)大于逃逸电场时, 宇宙线次级粒子中正、负电子的数目呈指数增长, 在大气深度约520 g/cm²处达到极大值, 与Gurevich等提出的相对论电子逃逸雪崩机理和Dwyer理论相符. 当雷暴电场强度小于逃逸电场时, 在所有负电场范围和大于600 V/cm的正电场范围, 总电子数目随电场强度的增大而增加; 当正电场小于400 V/cm时, 总电子数目均出现一定幅度的下降; 在电场为400–600 V/cm范围内, 总电子数目的变化与原初粒子的能量有关, 原初能量小于80 GeV时, 其次级粒子中总电子数目增加, 原初能量在80–120 GeV 范围内时, 总电子数目变化不明显, 原初能量大于120 GeV时, 总电子数目出现下降, 下降幅度约4%. 模拟结果可对羊八井ARGO实验的观测结果给予合理的解释.     

Highlights of the ARGO-YBJ Experiment at 4,300 m a.s.l.

The ARGO-YBJ experiment in Tibet, China has been operated to survey the northern sky for gamma ray sources, transient or steady, for nearly 6 years. Many astrophysics observational results will be highlighted in this paper, such as the sky survey results, extended source observation, diffuse gamma rays from the galactic plane, and emission mechanism of AGNs and their flares. As the unique detector for EAS with a continuously sensitive area of 5,600 m ², the ARGO-YBJ array catches almost all particles in the central part of showers. The high-quality data set for showers above few TeV has been used for cosmic ray measurements such as the energy spectrum and composition. All those results are summarized here. As one of the next generation ground-based high-altitude air shower detector, LHAASO is briefly introduced as the successor of ARGO-YBJ in the end of the paper.     

Atmospheric gamma rays in the energy region 40–1000 GeV

A large stack of lead-emulsion sandwich detector assembly was flown over Hyderabad, India. High energy gamma rays at the float altitude were unambiguously identified from the cascades they induced, and their energies reliably determined by improved methods. From an analysis of 163 gamma rays of energy ≳ 30 GeV, it is found that the differential energy spectrum is represented by the power lawJ _r (E)= 129·4E ^{−2·62±0·12} photons m⁻² sr⁻¹sec⁻¹ GeV⁻¹ at an effective atmospheric depth of 14·3 g cm⁻²; this is the first reliable balloon measurement of atmospheric gamma rays in the energy range 40–1000 GeV. After correcting for the gamma rays radiated by the primary cosmic ray electrons, the production spectrum of gamma rays, resulting from the collisions of cosmic ray nuclei with air nuclei, at the top of the atmosphere isP _r (E, 0)=8·2 × 10⁻⁴ E^2.60±0.09 photons g⁻¹sr⁻¹sec⁻¹ GeV⁻¹. The atmospheric propagation of the electromagnetic component due to the cascade process is also derived from the gamma ray production spectrum.     

Online charge calibration of LHAASO-WCDA——a study with the engineering array

LHAASO-WCDA is a large ground-based water Cherenkov detector array planned to be built at ShangriLa, Yunnan Province, China. As a major component of the LHAASO project, the main purpose of LHAASO-WCDA is to survey the northern sky for very-high-energy（above 100 GeV） gamma ray sources and measure the spectrum. To gain full knowledge of the water Cherenkov technique and to investigate the engineering issues, a 9-cell detector array has been built at the Yang-Ba-Jing site, neighboring the ARGO-YBJ experiment. With the array, charge calibration methods for both low and high ranges of the PMT readout are studied, whose result shows that a precision at several percentages can be reached, which can satisfy the requirement of the detector array. During the long term operation, the charge calibration stability and environmental afection are studied; in this paper, the results are discussed. These calibration methods are proposed to be applied in the future LHAASO-WCDA project.     

ARGO-YBJ实验“Scaler模式”计数的气象效应

对中意合作西藏ARGO\|YBJ实验“Scaler模式”下次级宇宙线计数的气象效应进行了讨论, 计算了计数率与大气压强、 室外温度、 大气电场及实验大厅内温度、 湿度等5个气象参量的偏相关系数。结果表明, 大气压强与次级宇宙线计数有很强的负相关, 与室外温度也有一定的负相关, 而实验大厅顶部的大气电场与实验记录的次级宇宙线计数基本没有关联。 另外, 实验大厅内温度也是影响次级宇宙线地面测量的一个重要因素, 实验大厅内的湿度也有一定影响。 随着符合多重数的增加, 实验大厅内温度和湿度的影响变得不再重要。 另外, 对次级宇宙线计数率进行了多参量的气象效应修正。 结果表明, 这种修正是可靠的, 为进一步利用ARGO\|YBJ实验“Scaler模式”下的实验数据进行各种物理分析打下了基础。     

太阳大耀斑期间甚高能粒子流强增加的一种机制

近年来,在太阳大耀班期间,由地面中子记录装置及地下不同深度μ子记录器记录到宇宙线粒子的短期增长(GLE)现象,其能量范围已达几百GeV,甚至可达TeV能区.本文讨论了TeV能区的增长现象可能是银河宇宙线部分粒子获得再加速,由于宇宙线粒子能谱很陡,几百GeV的再加速能量能使TeV以上能区宇宙线流强有明显增长.     

Radon emanation from soil samples

The soil or bedrock beneath a building is one of the sources of radon gas in the indoor air. The ²³⁸U content of samples of the soil or the bedrock can be measured by gamma ray spectrometry and is of interest because the uranium content in the soil is a precursor of the presence of the radon gas in the soil. The emanation of radon gas from different types of material can be estimated to some extent if the content of ²³⁸U of a sample is known and the ²²⁶Ra content is only minorly affected. The true emanation is, however, affected by various parameters. One of these parameters is the possibility or not for the gas to come out from the grains into the air in the space between the grains of the sample.

In this study we report the results from measurements of radon gas emanating from samples of soil frequent in the Lund region in Sweden and in the Barcelona region in Spain. As soils have different grain size it is important to know the type of soil. The ²³⁸U content of the soil is measured with gamma ray spectrometry. The radon measurements are made by Kodak plastic film in closed cans, filled with the soil according to a technique, developed for radon measurements in water samples.

The result shows, that the combination of grain size and uranium content is important for the emanation of the radon gas from the grains of the soil.     

Forbush decreases recorded by the URAGAN muon hodoscope in 2006–2011

Variations in the cosmic ray muon flux on Earth’s surface during Forbush decreases (FD) recorded by the URAGAN muon hodoscope in 2006–2011 are investigated. The dependence of the rate of amplitude reduction on the primary particle energy in a range above 10 GeV at different phases of FD development is studied by analyzing the variations in the cosmic ray muon flux recorded with the hodoscope. Analytical data on the spatial and angular dynamics of the muon flux are used to estimate variations in the spatial anisotropy of the muon flux during FDs.     

来自γ暴的甚高能γ射线

以膨胀火球模型解释来自γ暴的甚高能γ射线,其中考虑了高能γ射线产生效率,相对论效应以及宇宙背景辐射等因素,计算表明,大于10GeV的γ射线的喷射可能在火球膨胀开始后约10^－5s发生,其到达地面时的通量可达10^－4—10^－6cm^－2.     

Diffusion of cosmic rays in a model with interstellar turbulence damping due to interaction with energetic particles

A self-consistent model of galactic cosmic ray transport is considered. The resonance wave–particle interaction in this model causes a cascade of magnetosonic waves to decay in the interstellar medium. The calculated coefficient of diffusion of cosmic rays in the Galaxy has a characteristic minimum at an energy of several GeV/nucleon, which agrees with the empirical diffusion model of cosmic ray propagation.     

Estimating the fraction of gamma quanta in the primary cosmic ray flux with energies of ∼1017 eV from the MSU EAS array data

Using data from the MSU EAS array and model calculations, we search for events with abnormally small fractions of muons with energies above 10 GeV in showers with particle numbers of >2 × 10⁷ and zenith angles of <30 degrees. We confirm with good statistical accuracy that the content of gamma quanta in the primary cosmic ray flux can be as high as 2% at energies of ～10¹⁷ eV.     

Cosmic ray studies with the L3-cosmics program at CERN

The L3 detector at the CERN electron-positron collider had a muon spectrometer which was employed during the last years of LEP operation for cosmic ray studies. The results of this program include a precise muon spectrum and charge ratio between 20 GeV and 3 TeV, a limit on TeV primary antiprotons from a study of the Moon’s shadow, the (possible) observation of a are signal from a fixed position in the northern hemisphere through muons, a solar anisotropy of 200 GeV protons, and other results. Negative limits on muons associated with known H.E. gamma sources or gamma bursts, the search for anomalous H.E. interaction or decay events such as reported from the Kolar Gold Fields, and a search for muons correlated with a solar are are also noted.     

Dark Matter Particle Explorer observations of high-energy cosmic ray electrons plus positrons and their physical implications

The DArk Matter Particle Explorer(DAMPE) is a satellite-borne, high-energy particle and γ-ray detector, which is dedicated to indirectly detecting particle dark matter and studying high-energy astrophysics. The first results about precise measurement of the cosmic ray electron plus positron spectrum between 25 Ge V and 4.6 Te V were published recently. The DAMPE spectrum reveals an interesting spectral softening arount 0.9 Te V and a tentative peak around 1.4 Te V. These results have inspired extensive discussion. The detector of DAMPE, the data analysis, and the first results are introduced. In particular, the physical interpretations of the DAMPE data are reviewed.     

The Efficiency Mearurement of NaI(Tl) Detector for a Long Tube Volume Source of 6.13MeV Gamma-Ray

The relation of the ¹⁶N leak rate of the nuclear reactor to the efficiency and counting rate of γ–ray detector, velocity of high pressure vapor, is deduced. a conclusion of the efficiency independent on the velocity of high pressure vapor and decay constant of ¹⁶N is drawn. experimentally the space distribution of the relative efficiencies and the absolute efficiency at a refe~rence point are measured with Puc source emiting 6.13mev gamma ray detected by nai(tl) counter. The measured efficiency is consistent with monte carlo calculation in 7%. the compton small angle scattering contribution to the convergence length and the effect of the energy difference between 7.12mev and 6.13mev gamma ray on measured ¹⁶N leak rate are discussed.     

Gamma rays from dark matter annihilation in the Draco and observability at ARGO

The CACTUS experiment recently observed a gamma ray excess above 50 GeV from the direction of the Draco dwarf spheroidal galaxy. Considering that Draco is dark matter dominated, the gamma rays may be generated through dark matter annihilation in the Draco halo. In the framework of the minimal supersymmetric extension of the standard model we explore the parameter space to account for the gamma ray signals at CACTUS. We find that the neutralino mass is constrained to be approximately in the range between 100 GeV∼400 GeV and a sharp central cuspy of the dark halo profile in Draco is necessary to explain the CACTUS results. We then discuss further constraints on the supersymmetric parameter space by observations at the ground-based ARGO detector. It is found that the parameter space can be strongly constrained by ARGO if no excess from Draco is observed above 100 GeV.     

Small shower CORSIKA simulations

Extensive Air Showers (EAS) induced by cosmic ray particles of very low energies, owing to the significantly steep cosmic ray energy spectrum, dominate the secondary particle flux measured by single detectors and small shower arrays. Such arrays connected in extended networks can be used to determine potentially interesting spatial correlations between showers, which may shed new light on the nature of ultra high-energy cosmic rays. The quantitative interpretation of showers recorded by small local arrays requires a methodology that differs from that used by ordinary large EAS arrays operating in the "knee" region and above. We present "small EAS generator," a semi-analytical method for integrating cosmic ray spectra over energies of interest and summing over the mass spectra of primary nuclei in arbitrary detector configurations. Furthermore, we provide results on the EAS electron and muon fluxes and particle density spectra.     

The TeV-scale cosmic ray proton and helium spectra: Contributions from the local sources

Recent measurements of cosmic ray proton and helium spectra show a hardening above a few hundreds of GeV. This excess is hard to understand in the framework of the conventional models of galactic cosmic ray production and propagation. Here, we propose to explain this anomaly by the presence of local sources. Cosmic ray propagation is described as a diffusion process taking place inside a two-zone magnetic halo. We calculate the proton and helium fluxes at the Earth between 50 GeV and 100 TeV. Improving over a similar analysis, we consistently derive these fluxes by taking into account both local and remote sources for which a unique injection rate is assumed. We find cosmic ray propagation parameters for which the proton and helium spectra remarkably agree with the PAMELA and CREAM measurements over four decades in energy.