Elemental Spectra from the CREAM-I Flight

30TH INTERNATIONAL COSMIC RAY CONFERENCE Elemental Spectra from the CREAM-I Flight H. S. AHN , P. ALLISON , M. G. BAGLIESI , J. J. BEATTY , G. BIGONGIARI , P. BOYLE , J. T. CHILDERS , N. B. CONKLIN , S. COUTU , M. A. DUVERNOIS , O. GANEL , J. H. HAN , J. A. JEON , K. C. KIM , J. K. LEE , M. H. LEE , L. LUTZ , P. MAESTRO , A. MALININE , P. S. MARROCCHESI , S. MINNICK , S. I. MOGNET , S. NAM , S. NUTTER , I. H. PARK , N. H. PARK , E. S. SEO , R. SINA , S. SWORDY , S. WAKELY , J. WU , J. YANG , Y. S. YOON , R. ZEI , S. Y. ZINN . Inst. for Phys. Sci. and Tech., University of Maryland, College Park, MD 20742 USA Dept. of Physics, Ohio State University, Columbus, Ohio 43210, USA Dept. of Physics, University of Siena and INFN, Via Roma 56, 53100 Siena, Italy Enrico Fermi Institute and Dept. of Physics, University of Chicago, Chicago, IL 60637, USA School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA Dept. of Physics, Penn State University, University Park, PA 16802, USA Dept. of Physics, Ewha Womans University, Seoul, 120-750, Republic of Korea Dept. of Physics, Kent State University Tuscarawas, New Philadelphia, OH 44663, USA Dept. of Physics and Geology, Northern Kentucky University, Highland Heights, KY 41099, USA Dept. of Physics, University of Maryland, College Park, MD 20742 USA hsahn@umd.edu Abstract: The Cosmic Ray Energetics And Mass (CREAM) is a balloon-borne experiment designed to measure the composition and energy spectra of cosmic rays of charge Z = 1 to 26 up to an energy of 10 eV. CREAM had two successful flights on long-duration balloons (LDB) launched from Mc- Murdo Station, Antarctica, in December 2004 and December 2005. CREAM-I achieves a substantial measurement redundancy by employing multiple detector systems, namely a Timing Charge Detector and a Silicon Charge Detector (SCD) for particle identification, and a Transition Radiation Detector and a sampling tungsten/scintillating-fiber ionization calorimeter (CAL) for energy measurement. In this paper, preliminary energy spectra of various elements measured with CAL/SCD during the first 42-day flight are presented. Introduction The Cosmic Ray Energetics And Mass (CREAM) balloon-borne experiment is designed to investi- gate the charge and energy spectra of cosmic- ray nuclei of hydrogen to iron at high energies up to 10 eV. CREAM has had two success- ful long-duration balloon (LDB) flights, launched from McMurdo Station, Antarctica, for 42 days in 2004-2005 (CREAM-I) and 28 days in 2005-2006 (CREAM-II) [1]. In both flights CREAM em- ployed a 20 radiation length tungsten/scintillating- fiber sampling calorimeter (CAL), preceded by a pair of graphite targets providing 0.42 nu- clear interaction length, to induce hadronic show- ers from cosmic-ray nuclei, triggering and mea- suring the energy of those with energy above 10 eV. Each of the 20 active layers was seg- mented into 50 one-cm-wide ribbons. Signals from these ribbons were used to reconstruct and extrap- olate trajectories back to the Silicon Charge Detec- tor (SCD) of 52 56 pixels, for accurate charge measurement. Details of the experiment, including other complementary instruments, namely a Tim- ing Charge Detector and a Transition Radiation Detector, can be found in [2]. Various elements have been studied by analyzing the CREAM-I flight data with CAL/SCD. See [3] ELEMENTAL SPECTRA FROM THE CREAM-I FLIGHT for the spectra of hydrogen and helium. In this pa- per, preliminary energy spectra of cosmic-ray car- bon and oxygen are presented, and compared with results from other experiments. Calibration CAL was placed in one of CERN’s SPS accelerator beam-lines, and exposed to a variety of electron, proton, and nuclear fragment beams to verify both the instrument’s functionality and the validity of the simulation model. CAL responses to 150 GeV electrons were used for absolute calibration, which is extrapolated to the responses to much higher en- ergy cosmic rays collected during flight [4]. CREAM-I Flight During the flight, the payload floated at an aver- age altitude of 128,000 ft, corresponding to a resid- ual atmosphere of 3.9 g/cm . The analysis in this paper has been performed with only a subset of cosmic-ray events, CAL-triggered by requiring 6 consecutive layers to have energy deposit of more than 50 MeV in the highest deposit ribbon, and collected for 23.7 days when both CAL and SCD operation was stable. Live time fraction is assumed to be 75%. The dead CAL channels, noisy SCD pixels, and zero-suppression level in CAL ribbons have been taken into account in the detector simu- lations. Reconstruction Incident particle trajectory is estimated using fitting of a straight line through a combination of CAL hits with highest energy deposit in each layer, in x-z and y-z, respectively. The combination is chosen by rejecting any hit that is not consistent with others to make a straight line. This trajectory is further improved by including, in the fitting, (1) selected CAL hits’

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