Cosmic ray composition at high energies: Results from the TRACER project

The TRACER instrument Transition Radiation Array for Cosmic Energetic Radiation is designed to measure the individual energy spectra of cosmic-ray nuclei in long-duration balloon flights The large geometric factor of TRACER 5 m 2 sr permits statistically significant measurements at particle energies well beyond 10 14 eV TRACER identifies individual cosmic-ray nuclei with single-element resolution and measures their energy over a very wide range from about 0 5 to 10 000 GeV nucleon This is accomplished with a gas detector system of 1600 single-wire proportional tubes and plastic fiber radiators that measure specific ionization and transition radiation signals combined with plastic scintillators and acrylic Cherenkov counters A two-week flight in Antarctica in December 2003 has led to a measurement of the nuclear species oxygen to iron O Ne Mg Si S Ar Ca and Fe up to about 3 000 GeV nucleon We shall present the energy spectra and relative abundances for these elements and discuss the implication of the results in the context of current models of acceleration and propagation of galactic cosmic rays The instrument has been refurbished for a second long-duration flight in the Northern hemisphere scheduled for summer 2006 For this flight the dynamic range of TRACER has been extended to permit inclusion of the lighter elements B C and N in the measurement.Comment: 36th COSPAR Scientific Assembly. Held 16 - 23 July 2006, in Beijing, China., p.251

Cerenkov counters for high energy nuclei: Some new developments

A method to determine with gas Cerenkov counters the Lorentz factor, gamma = E/mc, of cosmic ray nuclei with high accuracy over the range gamma approx. 20 to 100 is discussed. The measurement of the Cerenkov emission angle theta, by use of a suitable imaging system is considered. Imaging counters, the ring imaging Cerenkov counters (RICH), were developed for use on accelerators. The image of off-axis particles to determine the amount of image distortion as a function of the direction of the incoming nucleus is examined and an acceptance solid angle, relative to the optical axis, within which the nucleus produces an image with an acceptable level of distortion is defined. The properties of the image, which becomes elliptical, for off-axis particles are analyzed

Cosmic Ray Nuclei (CRN) detector investigation

The Cosmic Ray Nuclei (CRN) detector was designed to measure elemental composition and energy spectra of cosmic radiation nuclei ranging from lithium to iron. CRN was flown as part of Spacelab 2 in 1985, and consisted of three basic components: a gas Cerenkov counter, a transition radiation detector, and plastic scintillators. The results of the experiment indicate that the relative abundance of elements in this range, traveling at near relativistic velocities, is similar to those reported at lower energy

A Comparative Study of the Depth of Maximum of Simulated Air Shower Longitudinal Profiles

A comparative study of simulated air shower longitudinal profiles is presented. An appropriate thinning level for the calculations is first determined empirically. High statistics results are then provided, over a wide energy range, (10^14.0 to 10^20.5 eV), for proton & iron primaries, using four combinations of the MOCCA & CORSIKA program frameworks, and the SIBYLL & QGSJET high energy hadronic interaction models. These results are compared to existing experimental data. The way in which the first interaction controls Xmax is investigated, as is the distribution of Xmax.Comment: 13 pages, 5 figures. Accepted by Astroparticle Physics. (Revised according to referee's comments.

High resolution charge measurements of UH cosmic ray nuclei using a direct imaging Cherenkov ground-based observatory

Journal ArticleThe accurate determination of the elemental composition of cosmic rays at high energies is expected to provide crucial clues on the origin of these particles. Here we discuss a technique that has become possible through the use of modern ground-based Cherenkov imaging detectors. We combine a measurement of the Cherenkov light produced by the incoming cosmic-ray nucleus in the upper atmosphere with an estimate of the total nucleus energy produced by the extensive air shower initiated when the particle interacts deeper in the atmosphere. The emission regions prior to and after the first nuclear interaction can be separated by an imaging Cherenkov system with sufficient angular and temporal resolution. Monte Carlo simulations indicate a widely space array of 10m diameter imaging Cherenkov detectors should have charge resolution of AZIZ <5% for incident iron nuclei in the region of the "knee" of the cosmic-ray energy spectrum. This technique also has the intriguing possibility to unambiguously discover nuclei heavier than iron at energies above 1014 eV. We describe a strawman detector design for a future observatory dedicated to high resolution cosmic ray measurements. This observatory can also serve as a wide field of view TeV gamma-ray survey instrument

Can We Observe the Quark Gluon Plasma in Cosmic Ray Showers ?

The possibility of detection of some features of high energy particle interactions with detectors placed at medium depths underground through studies on high energy muons is investigated. These muons carry information about the early interactions occurring during the development of the hadron cascade near the top of the atmosphere. They might reveal the effects resulting from creation of quark gluon plasma in interactions of ultra high energy cosmic ray iron nuclei with air nuclei.Comment: 16 pages, 8 figures, amended versio

Measurements of Compton Scattered Transition Radiation at High Lorentz Factors

X-ray transition radiation can be used to measure the Lorentz factor of relativistic particles. Standard transition radiation detectors (TRDs) typically incorporate thin plastic foil radiators and gas-filled x-ray detectors, and are sensitive up to \gamma ~ 10^4. To reach higher Lorentz factors (up to \gamma ~ 10^5), thicker, denser radiators can be used, which consequently produce x-rays of harder energies (>100 keV). At these energies, scintillator detectors are more efficient in detecting the hard x-rays, and Compton scattering of the x-rays out of the path of the particle becomes an important effect. The Compton scattering can be utilized to separate the transition radiation from the ionization background spatially. The use of conducting metal foils is predicted to yield enhanced signals compared to standard nonconducting plastic foils of the same dimensions. We have designed and built a Compton Scatter TRD optimized for high Lorentz factors and exposed it to high energy electrons at the CERN SPS. We present the results of the accelerator tests and comparisons to simulations, demonstrating 1) the effectiveness of the Compton Scatter TRD approach; 2) the performance of conducting aluminum foils; and 3) the ability of a TRD to measure energies approximately an order of magnitude higher than previously used in very high energy cosmic ray studies.Comment: 10 pages, 4 figures, To be published in NI

Elemental Composition of Cosmic Rays near the Knee by Multiparameter Measurement of Air Showerss

The small change in the spectral slope of the overall intensity of cosmic rays near 1 PeV may be associated with the endpoint energy of supernova shock acceleration. A crucial test of this connection and other ideas of the origin of the spectral `knee' is the reliable determination of the variation of elemental composition in this region. Recent measurements at the DICE/CASA/MIA air shower installation in Dugway, Utah, USA have provided several independent air shower parameters for each event. The derivation of elemental composition from a combination of Cherenkov size, depth of shower maximum in the atmosphere, muon size and electron size at ground level and the reliability of these results are discussed. There is no evidence from these data for a large change in the mean mass of cosmic rays across the `knee'. These measurements show the cosmic rays are composed of ~ 70% protons and alpha-particles near total energies of 10PeV.Comment: 29 pages including 10 figures Accepted for publication by Astroparticle Physics, 17th Sept. 199

Cosmic ray photodisintegration and the knee of the spectrum

We explore in some detail the scenario proposed to explain the observed knee of the cosmic ray (CR) spectrum as due to the effects of photodisintegration of the CR nuclei by interactions with optical and soft UV photons in the source region. We show that the photon column densities needed to explain the experimental data are significantly lower than those obtained in previous estimations which neglected multinucleon emission in the photodisintegration process. We also treat more accurately the photodisintegration thresholds, we discuss the effects of photopion production processes and the neutron escape mechanism, identifying the physical processes responsible for the qualitative features of the results. This scenario would require the CR nuclei to traverse column densities of $\sim 5 \times 10^{27}- 2 \times 10^{28}$ eV/cm$^2$ after being accelerated in order to reproduce the observed knee, and predicts that the CR composition should become lighter above $\sim 10^{16}$ eV.Comment: 17 pp. Comments and references added. To appear in Astroparticle Physic

A New Measurement of Cosmic Ray Composition at the Knee

The Dual Imaging Cerenkov Experiment (DICE) was designed and operated for making elemental composition measurements of cosmic rays near the knee of the spectrum at several PeV. Here we present the first results using this experiment from the measurement of the average location of the depth of shower maximum, , in the atmosphere as a function of particle energy. The value of near the instrument threshold of ~0.1 PeV is consistent with expectations from previous direct measurements. At higher energies there is little change in composition up to ~5 PeV. Above this energy is deeper than expected for a constant elemental composition implying the overall elemental composition is becoming lighter above the knee region. These results disagree with the idea that cosmic rays should become on average heavier above the knee. Instead they suggest a transition to a qualitatively different population of particles above 5 PeV.Comment: 7 pages, LaTeX, two eps figures, aas2pp4.sty and epsf.sty included, accepted by Ap.J. Let