Chemical Composition Of Cosmic Rays Research Articles

Chemical Composition of Cosmic Rays around the Knee Observed by the Tibet Air-Shower-Core Detector

Recent results and future prospects of the Tibet air-shower experiment are reported on the all-particle energy spectrum and the chemical composition of cosmic rays around 10 15 eV energy range. The knee of the all-particle energy spectrum has been clearly observed at the energy around 4 ×10 15 eV by Tibet III air-shower array located at Yangbajing, Tibet, China (atmospheric depth 606 g/cm 2 , area 37,000 m 2 ). The energy spectrum of light components (protons and helium) measured by air-shower-core detector exhibits steeper power index than that of direct measurements below 10 14 eV, leading to decreasing fraction of the light component toward the knee. Hence, it is strongly suggested that the origin of the knee is related with the change of the chemical composition of cosmic rays. A new air-shower-core detector called `YAC' is under the preparation for explicit measurement of the heavy component.

Calibration of the Yangbajing Air-shower Core detector using the test beam of BEPCII

Yangbajing Air shower Core detector(YAC) has been developed for the next phase of Tibet air-shower experiment to measure the chemical composition of cosmic rays in “knee” region. A preparation is made for calibration of the linearity of the dynamic range and position dependence of light yield of YAC using test beam of BEPCII. A scraper will be used to attenuate the electron beam intensity from about 10 10 /pulse to 10 2 –10 6 /pulse. A Faraday cup, a thick ionization chamber and a thin ionization chamber are being manufactured to monitor the beam intensity covering dynamic range from 10 2 /pulse to 10 10 /pulse.

Cosmic ray data and their interpretation: about the Tibet Shower Array: Chemical Composition of Cosmic Rays at the Knee Viewed from the Tibet Air Shower Experiment

A brief summary is given about present status of composition measurement of cosmic rays by direct observations and indirect ones which provides key information on the origin of the cosmic rays. The result of Tibet hybrid experiment measuring proton and helium spectra at the knee is presented, in which the decreasing fractions of both of the proton and helium component to the all particle spectrum with increasing energy are observed suggesting that the knee is dominated by heavy nuclei. It is planed to explicitly measure the iron spectrum at the knee by detecting the core structure of the air showers in the next phase of Tibet experiment ‘YAC’ ( Y angbajing A ir shower C ore array).

Underground cosmic-ray experiment EMMA

A new cosmic-ray experiment is under construction in the Pyhasalmi mine, Finland. It aims to study the chemical composition of cosmic rays at and above the knee region. The array, called EMMA, will cover approximately 150 m2 of detector area at the depth of 85 metres ( ∼ 240 mwe ). It is capable of measuring the multiplicity and the lateral distribution of underground muons, and the arrival direction of the air shower. The full-size array is expected to be ready by the end of 2007. A partial-size array (one third of the full size) is planned to record data already at the first quarter of 2007. The array is also expected to be capable of measuring such high-multiplicity muon bundles as was observed at the cosmic-ray experiments at the LEP detectors.

Measuring the chemical composition of cosmic rays with AMS

AMS (Alpha Magnetic Spectrometer) is a particle detector designed to operate at the International Space Station. Starting in 2008, its purpose is to perform accurate, high statistics, long duration measurements of energetic (0.1 GeV to TeV) charged cosmic ray spectra in space, providing fundamental information about key ingredients in the spallation reactions taking place in the interstellar medium. We present here the characteristics of this experiment and the extense collaboration supporting the project.

Seyfert nuclei as sources of ultrahigh-energy cosmic rays

Particles can be accelerated to ultrahigh energies E≈1021 eV in moderate Seyfert nuclei. This acceleration occurs in shock fronts in relativistic jets. The maximum energy and chemical composition of the accelerated particles depend on the magnetic field in the jet, which is not well known; fields in the range ∼5–1000 G are considered in the model. The highest energies of E≈1021 eV are acquired by Fe nuclei when the field in the jet is B≈16 G. When B∼(5–40) G, nuclei with Z<10 are accelerated to E≤1020 eV, while nuclei with Z≥10 acquire energies E≥2×1020 eV. Only particles with Z≥23 acquire energies E≤1020 eV when B∼1000 G. Protons are accelerated to E<4×1019 eV, and do not fall into the range of energies of interest for any magnetic field B. The particles lose a negligible amount of their energy in interactions with infrared photons in the accretion disk; losses in the thick gas-dust torus are also negligible if the luminosity of the galaxy is L≤1046 erg/s and the angle between the normal to the galactic plane and the line of sight is sufficiently small, i.e., if the axial ratio of the galactic disk is comparatively high. The particles do not lose energy to curvature radiation if their deviations from the jet axis do not exceed 0.03–0.04 pc at distances from the center of R≈40–50 pc. Synchrotron losses are small, since the magnetic field frozen in the galactic wind at R≤40–50 pc is directed (as in the jet) primarily in the direction of motion. If the model considered is valid, the detected cosmic-ray protons could be either fragments of Seyfert nuclei or be accelerated in other sources. The jet magnetic fields can be estimated both from direct astronomical observations and from the energy spectrum and chemical composition of cosmic rays.

Detecting radio emission from cosmic ray air showers and neutrinos with a digital radio telescope

We discuss the possibilities of measuring ultra-high energy cosmic rays and neutrinos with radio techniques. We review a few of the properties of radio emission from cosmic ray air showers and show how these properties can be explained by coherent “geosynchrotron” emission from electron–positron pairs in the shower as they move through the geomagnetic field. This should allow one to use the radio emission as a useful diagnostic tool for cosmic ray research. A new generation of digital telescopes will make it possible to study this radio emission in greater detail. For example, the planned low-frequency array (LOFAR), operating at 10–200 MHz, will be an instrument uniquely suited to study extensive air showers and even detect neutrino-induced showers on the moon. We discuss sensitivities, count rates and possible detection algorithms for LOFAR and a currently funded prototype station LOPES. This should also be applicable to other future digital radio telescopes such as the Square Kilometer Array (SKA). LOFAR will be capable of detecting air-shower radio emission from >2×10 14 to ∼10 20 eV. The technique could be easily extended to include air shower arrays consisting of particle detectors (KASCADE, Auger), thus providing crucial additional information for obtaining energy and chemical composition of cosmic rays. It also has the potential to extend the cosmic ray search well beyond an energy of 10 21 eV if isotropic radio signatures can be found. Other issues that LOFAR can address are to determine the neutral component of the cosmic ray spectrum, possibly look for neutron bursts, and do actual cosmic ray astronomy.

High energy cosmic ray composition

Cosmic rays are understood to result from energetic processes in the galaxy, probably from supernova explosions. However, cosmic ray energies extend several orders of magnitude beyond the limit thought possible for supernova blast waves. Over the past decade several ground-based and space-based investigations were initiated to look for evidence of a limit to supernova acceleration in the cosmic-ray chemical composition at high energies. These high-energy measurements are difficult because of the very low particle fluxes in the most interesting regions. The space-based detectors must be large enough to collect adequate statistics, yet stay within the weight limit for space flight. Innovative approaches now promise high quality measurements over an energy range that was not previously possible. The current status of high energy cosmic-ray composition measurements and planned future missions are discussed in this paper.

A model of particle acceleration to high energies by multiple supernova explosions in OB associations

The possibility of cosmic-ray (CR) acceleration to energies above 109 GeV per nucleus in extended Galactic OB associations is analyzed. A two-stage acceleration mechanism is justified: at the first stage, the acceleration by separate shock fronts from spatially and temporally correlated supernovae explosions takes place, and, at the second stage, the Fermi acceleration by supersonic turbulence in an extended, strongly perturbed region near the OB association takes place. We calculate the CR energy spectrum, the change in CR chemical composition with energy, and the energy dependence of the mean logarithm of atomic mass, ‹lnA›, for the accelerated particles. The calculated values are compared with those observed near the break in the energy spectrum. We estimate the turbulence parameters, which allow the observed features of the energy spectrum and the CR enrichment with heavy elements to be explained.

Monte Carlo simulation of air shower development for the study of cosmic ray composition

We have developed a Monte Carlo program to simulate the extensive air showers (EASs) in short computing time and to study the chemical composition of cosmic rays at the knee region. This code is particularly applied to the C ̌ erenkov experiment that measures the time structure of C ̌ erenkov light from the EAS. There are many EAS programs available for public use. However, they are not adequate for simulating large number of air shower, since they deal with the very complex interaction algorithm and consume a lot of time. Therefore much faster program should be developed adequately for our purpose. In this report, we discuss the interaction model used in our Monte Carlo code and make a comparison with the accelerator data and the widely used Monte Carlo code, CORSIKA. In addition, we propose a parameterization method that describes the fluctuation of air shower development. Using this method, we can calculate air shower development 10 6 times faster than the CORSIKA simulation code.

Cosmic ray proton spectrum determined with the imaging atmospheric Cherenkov technique

The HEGRA system of 4 imaging atmospheric Cherenkov telescopes ~IACTs! has been used to determine the flux and the spectrum of cosmic ray protons over a limited energy range around 1.5 TeV. Although the IACT system is designed for the detection of g-rays with energies above 500 GeV, it has also a large detection area of .10 6 m 2 33 msr for primary protons of energies above 1 TeV and the capability to reconstruct the primary proton energy with a reasonable accuracy DE/E of 50% near this threshold. Furthermore, the principle of stereoscopic detection of air showers permits the effective suppression of air showers induced by heavier primaries already on the trigger level, and in addition on the software level by analysis of the stereoscopic images. The combination of both capabilities permits a determination of the proton spectrum almost independently of the cosmic ray chemical composition. The accuracy of our estimate of the spectral index at 1.5 TeV is limited by systematic uncertainties and is comparable to the accuracy achieved with recent balloon and space borne experiments. In this paper we describe in detail the analysis tools, namely the detailed Monte Carlo simulation, the analysis procedure and the results. We determine the local ~i.e., in the range of 1.5‐3 TeV! differential spectral index to be g p52.7260.02stat60.15syst and obtain an integral flux above 1.5 TeV of F (.1.5 TeV)53.160.6 stat61.2syst310 22 /s sr m 2 . @S0556-2821~99!04107-7#

Status and Results from the HEGRA Air Shower Experiment

The HEGRA experiment investigates the relativistic (non thermal) universe by measuring air showers initiated in the atmosphere by photons and charged particles from the cosmos, using the imaging atmospheric Cherenkov light technique (> 500 GeV) and the showerfront sampling technique (> 20 TeV). New results concerning the search and study of gamma ray sources above 500 GeV, the measurement of the energy spectrum and chemical composition of cosmic rays above 1 PeV and the search of TeV counterparts of Gamma Ray Bursts are briefly described.

Estimate of the chemical composition of cosmic rays from a multifractal moments analysis of the lateral particle distributions in the core of high-energy EAS

The central detector of the KASCADE experiment, which is focused to investigate the chemical composition of primary cosmic rays by EAS observations in the energy range of 1014 eV to 1017 eV, is able to observe the density distributions of the EAS components in the shower core, in particular of the muons by large-area position-sensitive multiwire proportional chambers (MWPC), installed below an iron sampling calorimeter (≈ 1000 g/cm2 Fe) used for hadron measurements. Using a method based on the determination of multifractal moments the appearance of the density distributions of the EAS core in the MWPC has been analyzed. Results with EAS simulations indicate distinct signatures for the mass of the primary. We communicate first results extracted from measurements with the MWPC combined with measurements of the energy deposit in the timing and trigger facility (segmented scintillation detector plane as third active layer of the calorimeter) of the KASCADE central detector.

Muons (>or=1 GeV) in large extensive air showers of energies between 1016.5 eV and 1019.5 eV observed at Akeno

The properties of muons (>or=1 GeV) in giant air showers between 1016.5 eV and 1019.5 eV are measured by the Akeno 1 km2, 20 km2 and 100 km2 air shower arrays. The lateral distribution of muons is well fitted by the formula given by Greisen (1960) with parameters beta =2.52+or-0.02 and log(R0)=(0.58+or-0.04) (sec theta -1)+(2.39+or-0.05) between 1016.5 eV and 1019.0 eV within 800 m of the air shower axis, where theta is the zenith angle of the shower arrival direction. The relation between the total number of muons (Nmu ) and the total number of electrons (Ne) derived using these parameters is expressed on average as Nmu =(2:6+or-1.3)*105.0+ alpha (Ne/107)b where alpha =(1.07+or-0.13) (sec theta -1) and b=(0.77+or-0.02)-(0.17+or-0.02) (sec theta -1). The lateral distribution of muons becomes steeper than expected from extrapolation of the above formula for core distances >800 m and is expressed as rho mu =Nmu (C'mu /R02)r-0.75 (1+r)- beta (1+(R/800 m)3)- delta (r=R/R0, where R is a core distance). No deviation from this formula has been observed for sec theta <2.0 up to 1019.0 eV. The relation between the muon density (S(600)) and the charged-particle density on the ground at 600 m from the core (S(600)) is studied between 1016.5 eV and 1019.0 eV. A systematic change in the chemical composition of cosmic rays from a predominantly heavy to a predominantly light composition above 1017.5 eV claimed by the Fly's Eye group has not been detected beyond the present experimental uncertainties. The present experiment suggests a much smaller rate of change of composition between 1017.5 eV and 1018.5 eV than that from the Fly's Eye experiment.

Design and performance of the angle integrating Čerenkov array AIROBICC

Abstract An air-shower array consisting of 49 open huts with photomultiplier tubes viewing the night sky over a solid angle of about 1 steradian is described. The array is operating in conjunction with the HEGRA installation. The main objectives of the experiment are VHE to UHE γ-ray astronomy and a determination of the chemical composition of cosmic rays. The design principles, construction and performance in angular resolution, energy threshold and determination of shower parameters are discussed.

The origin of cosmic rays

The search for the origin of cosmic rays is a quest of almost a hundred years. A recent theoretical proposal gives quantitative predictions, which can be tested with data. Specifically, it has been suggested, that all cosmic rays can be attributed to just three source sites: i) supernova explosions into the interstellar medium, ii) supernova explosions into a stellar wind, and iii) powerful radiogalaxies. The cosmic rays from any extragalactic source suffer from interaction with the microwave background, leading to the Greisen-Zatsepin-Kuzmin cutoff. While the particle energies, the spectrum and the chemical composition of cosmic rays over the energy range from about GeV to about 100 EeV can be interpreted in the theory, there are exciting measurements now: New measurements show that there are cosmic ray events beyond the Greisen-Zatsepin-Kuzmin cutoff. We discuss here possible sources, and specifically ask whether powerful radiogalaxies are suitable candidates. The basic concepts used here are the minimal hypothesis that the intergalactic magnetic field is given by the galaxy distribution, and the observation that radio galaxies also cluster like galaxies.

Cosmic ray chemical composition estimated between 2 × 1014 eV and 2 × 1016 eV using muon size fluctuations

Accurate measurement of the total number of muons in an air shower is important for estimating the cosmic ray chemical composition. In order to translate this view into action, we have constructed an air shower array at Ohya. Many large muon detectors have been deployed in the stone mine and the total area amounts to about 400 m 2 . At the ground surface, scintillation counters have been deployed for determining the shower size and arrival direction of an air shower. From the data obtained, we estimated the cosmic ray chemical composition between 2 × 10 14 eV and 2 × 10 16 eV, which includes the well known spectrum's “knee”. As a method of estimation, we took the muon size fluctuation. The estimated rate of protons becomes relatively low, and that of helium nuclei increases, above an energy of 2 × 10 15 eV. Also, the fraction of very heavy nuclei such as iron increases above this energy.

Measuring the chemical composition of cosmic rays at ? 1013?1015 eV by utilizing the solar and geomagnetic fields

According to a proposal of Lloyd-Evans (1985), the average charge of particles in the cosmic radiation near 1014eV can be determined by observing the effect of the solar magnetic field on the Sun's shadow in the angular distribution of energetic primary cosmic ray particles. This suggestion is shown to be realizable with a new type of EAS-array proposed for the purpose of high energy γ-ray astronomy. The same measurement provides information on the integrated strength of the solar magnetic field. As the array will be sensitive and provide good angular resolution down to a few times 1012eV, more detailed results on the primary composition near 1013eV can be obtained by investigating the shape of the shadow of the Moon as affected by the geomagnetic field.

The origin of cosmic rays as viewed from their source composition

Based on the fact that the chemical composition of cosmic rays in their sources is similar to that of the interstellar clouds or grains which are relatively rich in refractory and siderophile elements as compared to the chemical composition of the solar atmosphere, it is shown that cosmic ray source matter can be identified as the dusts or grains observed in the envelope of red supergiants or the matter originally ejected from supernova explosions and that it must have passed through a state as reaching to 1000K or less in temperature.

Analytic representation of the proton-proton and proton-nucleus cross-sections and its application to the sea-level spectrum and charge ratio of muons

We have calculated the sea-level differential muon momentum spectrum and their charge ratio from 1 GeV/c to 5000 GeV/c, using all of the available accelerator data. We find an excellent agreement between our calculation and the existing experimental data. We see no need, at present, to invoke any change either in the cosmic-ray chemical composition or in the nature of the hadron-nucleus interaction at hadron energies above 1500 GeV.