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COSMIC-RAY PROTON AND HELIUM SPECTRA FROM THE FIRST CREAM FLIGHT
Yoon, Y. S.,Ahn, H. S.,Allison, P. S.,Bagliesi, M. G.,Beatty, J. J.,Bigongiari, G.,Boyle, P. J.,Childers, J. T.,Conklin, N. B.,Coutu, S.,DuVernois, M. A.,Ganel, O.,Han, J. H.,Jeon, J. A.,Kim, K. C.,Le IOP Publishing 2011 The Astrophysical journal Vol.728 No.2
<P>Cosmic-ray proton and helium spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass experiment flown for 42 days in Antarctica in the 2004-2005 austral summer season. High-energy cosmic-ray data were collected at an average altitude of similar to 38.5 km with an average atmospheric overburden of similar to 3.9 g cm(-2). Individual elements are clearly separated with a charge resolution of similar to 0.15 e (in charge units) and similar to 0.2 e for protons and helium nuclei, respectively. The measured spectra at the top of the atmosphere are represented by power laws with a spectral index of -2.66 +/- 0.02 for protons from 2.5 TeV to 250 TeV and -2.58 +/- 0.02 for helium nuclei from 630 GeV nucleon(-1) to 63 TeV nucleon-1. They are harder than previous measurements at a few tens of GeV nucleon-1. The helium flux is higher than that expected from the extrapolation of the power law fitted to the lower-energy data. The relative abundance of protons to helium nuclei is 9.1 +/- 0.5 for the range from 2.5 TeV nucleon(-1) to 63 TeV nucleon(-1). This ratio is considerably smaller than the previous measurements at a few tens of GeV nucleon(-1).</P>
DISCREPANT HARDENING OBSERVED IN COSMIC-RAY ELEMENTAL SPECTRA
Ahn, H. S.,Allison, P.,Bagliesi, M. G.,Beatty, J. J.,Bigongiari, G.,Childers, J. T.,Conklin, N. B.,Coutu, S.,DuVernois, M. A.,Ganel, O.,Han, J. H.,Jeon, J. A.,Kim, K. C.,Lee, M. H.,Lutz, L.,Maestro, P IOP Publishing 2010 ASTROPHYSICAL JOURNAL LETTERS - Vol.714 No.1
<P>The balloon-borne Cosmic Ray Energetics And Mass experiment launched five times from Antarctica has achieved a cumulative flight duration of about 156 days above 99.5% of the atmosphere. The instrument is configured with complementary and redundant particle detectors designed to extend direct measurements of cosmic-ray composition to the highest energies practical with balloon flights. All elements from protons to iron nuclei are separated with excellent charge resolution. Here, we report results from the first two flights of similar to 70 days, which indicate hardening of the elemental spectra above similar to 200 GeV/nucleon and a spectral difference between the two most abundant species, protons and helium nuclei. These results challenge the view that cosmic-ray spectra are simple power laws below the so-called knee at similar to 10(15) eV. This discrepant hardening may result from a relatively nearby source, or it could represent spectral concavity caused by interactions of cosmic rays with the accelerating shock. Other possible explanations should also be investigated.</P>
MEASUREMENTS OF THE RELATIVE ABUNDANCES OF HIGH-ENERGY COSMIC-RAY NUCLEI IN THE TeV/NUCLEON REGION
Ahn, H. S.,Allison, P. S.,Bagliesi, M. G.,Barbier, L.,Beatty, J. J.,Bigongiari, G.,Brandt, T. J.,Childers, J. T.,Conklin, N. B.,Coutu, S.,DuVernois, M. A.,Ganel, O.,Han, J. H.,Jeon, J. A.,Kim, K. C.,L IOP Publishing 2010 The Astrophysical journal Vol.715 No.2
<P>We present measurements of the relative abundances of cosmic-ray nuclei in the energy range of 500-3980 GeV/nucleon from the second flight of the Cosmic Ray Energetics And Mass balloon-borne experiment. Particle energy was determined using a sampling tungsten/scintillating-fiber calorimeter, while particle charge was identified precisely with a dual-layer silicon charge detector installed for this flight. The resulting element ratios C/O, N/O, Ne/O, Mg/O, Si/O, and Fe/O at the top of atmosphere are 0.919 +/- 0.123(stat) +/- 0.030(syst), 0.076 +/- 0.019(stat) +/- 0.013(syst), 0.115 +/- 0.031(stat) +/- 0.004(syst), 0.153 +/- 0.039(stat) +/- 0.005(syst), 0.180 +/- 0.045(stat) +/- 0.006(syst), and 0.139 +/- 0.043(stat) +/- 0.005(syst), respectively, which agree with measurements at lower energies. The source abundance of N/O is found to be 0.054 +/- 0.013(stat) +/- 0.009(-0.017)(syst+0.010esc). The cosmic-ray source abundances are compared to local Galactic (LG) abundances as a function of first ionization potential and as a function of condensation temperature. At high energies the trend that the cosmic-ray source abundances at large ionization potential or low condensation temperature are suppressed compared to their LG abundances continues. Therefore, the injection mechanism must be the same at TeV/nucleon energies as at the lower energies measured by HEAO-3, CRN, and TRACER. Furthermore, the cosmic-ray source abundances are compared to a mixture of 80% solar system abundances and 20% massive stellar outflow (MSO) as a function of atomic mass. The good agreement with TIGER measurements at lower energies confirms the existence of a substantial fraction of MSO material required in the similar to TeV per nucleon region.</P>
ENERGY SPECTRA OF COSMIC-RAY NUCLEI AT HIGH ENERGIES
Ahn, H. S.,Allison, P.,Bagliesi, M. G.,Barbier, L.,Beatty, J. J.,Bigongiari, G.,Brandt, T. J.,Childers, J. T.,Conklin, N. B.,Coutu, S.,DuVernois, M. A.,Ganel, O.,Han, J. H.,Jeon, J. A.,Kim, K. C.,Lee, IOP Publishing 2009 The Astrophysical journal Vol.707 No.1
<P>We present new measurements of the energy spectra of cosmic-ray (CR) nuclei from the second flight of the balloon-borne experiment Cosmic-Ray Energetics And Mass (CREAM). The instrument included different particle detectors to provide redundant charge identification and measure the energy of CRs up to several hundred TeV. The measured individual energy spectra of C, O, Ne, Mg, Si, and Fe are presented up to similar to 10(14) eV. The spectral shape looks nearly the same for these primary elements and it can be fitted to an E(-2.66 +/- 0.04)power law in energy. Moreover, a new measurement of the absolute intensity of nitrogen in the 100-800 GeV/n energy range with smaller errors than previous observations, clearly indicates a hardening of the spectrum at high energy. The relative abundance of N/O at the top of the atmosphere is measured to be 0.080 +/- 0.025 (stat.) +/- 0.025 (sys.) at similar to 800 GeV/n, in good agreement with a recent result from the first CREAM flight.</P>
Performance of a Dual Layer Silicon Charge Detector During CREAM Balloon Flight
Nam, S.,Ahn, H. S.,Allison, P.,Bagliesi, M. G.,Barbier, L.,Beatty, J. J.,Bigongiari, G.,Brandt, T. J.,Jeon, J. A.,Childers, J. T.,Conklin, N. B.,Coutu, S.,DuVernois, M. A.,Ganel, O.,Han, J. H.,Kim, K. IEEE 2007 IEEE transactions on nuclear science Vol.54 No.5
<P>The balloon-borne cosmic-ray experiment CREAM (Cosmic Ray Energetics And Mass) has completed two flights in Antarctica, with a combined duration of 70 days. One of the detectors in the payload is the SCD (silicon charge detector) that measures the charge of high energy cosmic rays. The SCD was assembled with silicon sensors. A sensor is a 4 × 4 array of DC-coupled PIN diode pixels with the total active area of 21 × 16 mm<SUP>2</SUP>. The SCD used during the first flight (December 2004-January 2005) was a single layer device, then upgraded to a dual layer device for the second flight (December 2005-January 2006), covering the total sensitive area of 779 × 795 mm<SUP>2</SUP>. Flight data demonstrated that adding a second layer improved SCD performance, showing excellent particle charge resolution. With a total dissipation of 136 W for the dual layer system, special care was needed in designing thermal paths to keep the detector temperature within its operational range. As a consequence, flight temperatures of the SCD, even at diurnal maximum were kept below 38°C. The SCD mechanical structure was designed to minimize the possibility of damage to the sensors and electronics from the impacts of parachute deployment and landing. The detector was recovered successfully following the flight and is being refurbished for the next flight in 2007. Details of construction, operation, and performance are presented for the dual-layered SCD flown for the second CREAM flight.</P>
Ahn, H.S.,Allison, P.S.,Bagliesi, M.G.,Beatty, J.J.,Bigongiari, G.,Boyle, P.J.,Brandt, T.J.,Childers, J.T.,Conklin, N.B.,Coutu, S.,Duvernois, M.A.,Ganel, O.,Han, J.H.,Hyun, H.J.,Jeon, J.A.,Kim, K.C.,L North-Holland ; Elsevier Science Ltd 2008 Astroparticle physics Vol.30 No.3
We present new measurements of heavy cosmic-ray nuclei at high energies performed during the first flight of the balloon-borne cosmic-ray experiment Cosmic-Ray Energetics and Mass (CREAM). This instrument uses multiple charge detectors and a transition radiation detector to provide the first high accuracy measurements of the relative abundances of elements from boron to oxygen up to energies around 1TeV/n. The data agree with previous measurements at lower energies and show a relatively steep decline (∼E<SUP>-0.6</SUP> to E<SUP>-0.5</SUP>) at high energies. They further show the source abundance of nitrogen relative to oxygen is ∼10% in the TeV/n region.
Approaching the Spectral Knee in High Energy Cosmic Rays with CREAM
S. Seo, E.,S. Ahn, H.,Allison, P.,Anderson, T.,G. Bagliesi, M.,Barbier, L.,Barrau, A.,Bazer-Bachi, R.,J. Beatty, J.,Bigongiari, G.,Bhoyar, P.,Boyle, P.,T. Brandt, T.,Bué,nerd, M.,B. Conklin, N. Physical Society of Japan 2009 Journal of the Physical Society of Japan Vol.78 No.suppl