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 ~38.5 km with an average atmospheric overburden of ~3.9 g cm--2. Individual elements are clearly separated with a charge resolution of ~0.15 e (in charge units) and ~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.
We present a new measurement of the cosmic-ray positron fraction at energies between 5 and 15 GeV with the balloon-borne HEAT-pbar instrument in the spring of 2000. The data presented here are ...compatible with our previous measurements, obtained with a different instrument. The combined data from the three HEAT flights indicate a small positron flux of nonstandard origin above 5 GeV. We compare the new measurement with earlier data obtained with the HEAT-e(+/-) instrument, during the opposite epoch of the solar cycle, and conclude that our measurements do not support predictions of charge sign dependent solar modulation of the positron abundance at 5 GeV.
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 ~1014 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 ~800 GeV/n, in good agreement with a recent result from the first CREAM flight.
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{sup stat} {+-} 0.030{sup syst}, 0.076 {+-} 0.019{sup stat} {+-} 0.013{sup syst}, 0.115 {+-} 0.031{sup stat} {+-} 0.004{sup syst}, 0.153 {+-} 0.039{sup stat} {+-} 0.005{sup syst}, 0.180 {+-} 0.045{sup stat} {+-} 0.006{sup syst}, and 0.139 {+-} 0.043{sup stat} {+-} 0.005{sup syst}, respectively, which agree with measurements at lower energies. The source abundance of N/O is found to be 0.054 {+-} 0.013{sup stat} {+-} 0.009{sup syst+0.010esc} {sub -0.017}. 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 {approx}TeV per nucleon region.
The cosmic-ray energetics and mass (CREAM) investigation is designed to measure cosmic-ray composition to the supernova energy scale of 10
15 eV in a series of ultra long duration balloon (ULDB) ...flights. The first flight is planned to be launched from Antarctica in December 2004. The goal is to observe cosmic-ray spectral features and/or abundance changes that might signify a limit to supernova acceleration. The particle charge (
Z) measurements will be made with a timing-based charge detector and a pixelated silicon charge detector to minimize the effect of backscatter from the calorimeter. The particle energy measurements will be made with a transition radiation detector (TRD) for
Z>3 and a sampling tungsten/scintillator calorimeter for
Z⩾1 particles, allowing inflight cross calibration of the two detectors. The status of the payload construction and flight preparation are reported in this paper.
We present a new measurement of the antiproton-to-proton abundance ratio, pbar/p, in the cosmic radiation. The HEAT-pbar instrument, a balloon borne magnet spectrometer with precise rigidity and ...multiple energy loss measurement capability, was flown successfully in Spring 2000, at an average atmospheric depth of 7.2 g/cm(2). A total of 71 antiprotons were identified above the vertical geomagnetic cutoff rigidity of 4.2 GV. The highest measured proton energy was 81 GeV. We find that the pbar/p abundance ratio agrees with that expected from a purely secondary origin of antiprotons produced by primary protons with a standard soft energy spectrum.
The Cosmic Ray Energetics and Mass (CREAM) timing charge detector Ahn, H.S.; Allison, P.S.; Bagliesi, M.G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2009, Letnik:
602, Številka:
2
Journal Article
Recenzirano
The use of detectors based on plastic scintillator with photomultiplier tubes (PMTs) is common in cosmic-ray experiments to differentiate particle charges. However, in the presence of a calorimeter, ...the standard method of pulse charge integration over a time longer than a PMT pulse is hampered by abundant albedo particles. The Cosmic Ray Energetics and Mass (CREAM) instrument surmounts this problem by measuring the peak voltage of the PMT pulse within
∼
3
ns
of a threshold crossing in the readout of a timing charge detector (TCD). The design and performance of the TCD is presented. A charge resolution of
0.2
e
for oxygen and
0.4
e
for iron is obtained for through-going cosmic-ray particles.
The Cosmic-Ray Energetics And Mass balloon-borne experiment has been launched twice in Antarctica, first in December 2004 and again in December 2005. It circumnavigated the South Pole three times ...during the first flight, which set a flight duration record of 42 days. A cumulative duration of 70 days within 13 months was achieved when the second flight completed 28 days during two circumnavigations of the Pole on 13 January 2006. Both the science instrument and support systems functioned extremely well, and a total 117
GB of data including 67 million science events were collected during these two flights. Preliminary analysis indicates that the data extend well above 100
TeV and follow reasonable power laws. The payload recovered from the first flight has been refurbished for the third flight in 2007, whereas the payload from the second flight is being refurbished to be ready for the fourth flight in 2008. Each flight will extend the reach of precise cosmic-ray composition measurements to energies not previously possible.
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