New Measurement of the Cosmic-Ray Positron Fraction from 5 to 15 GeV

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 non-standard 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.Comment: accepted for publication in PR

Characterization and expression analysis of the groESL operon of Bartonella bacilliformis

The groESL operon of Bartonella bacilliformis, a facultative intracellular, Gram-negative bacterium and etiologic agent of Oroya Fever, was characterized. Sequence analysis revealed an operon containing two genes of 294 (groES) and 1632 nucleotides (groEL) separated by a 55-nt intergenic spacer. The operon is preceded by a 72-nt ORF (ORF1) that encodes a hypothetical protein with homology to a portion of the HrcA repressor for groESL. A divergent fumarate hydratase C (fumC) gene lies further upstream. Deduced amino acid sequences for B. bacilliformis GroEL and GroES revealed a high degree of identity with homologues from other Bartonella and alpha-Protebacteria. A single transcriptional start site (TSS) was mapped 79 nucleotides upstream of the groES start codon, regardless of incubation temperature. The TSS was located immediately 5\u27 to a potential controlling inverted repeat of chaperonin expression (CIRCE) element and is preceded by a sigma70-like promoter. The operon is followed by a predicted rho-independent transcriptional terminator. Northern blot analysis indicated that groES and groEL are co-transcribed as a single mRNA of approximately 2.4 kb. A 6-h time course analysis by qRT-PCR showed that groEL expression increases 1.3-fold within 30 min of a temperature upshift from 30 to 37 degrees C, with maximum transcription reached after 60 min (approximately 4.3-fold), followed by a steady decrease to background (30 degrees C) transcription levels by 6 h. Western blot analysis revealed a 1.4- and 1.5-fold increase in GroEL synthesis following a temperature upshift or by inhibiting DNA supercoiling with coumermycin A1, respectively. Functional expression and complementation of temperature-sensitive Escherichia coli groES or groEL mutants with the cloned operon allowed them to grow at otherwise restrictive temperatures

Elemental energy spectra of cosmic rays measured by CREAM-II

We present new measurements of the energy spectra of cosmic-ray (CR) nuclei from the second flight of the balloon-borne experiment CREAM (Cosmic Ray Energetics And Mass). The instrument (CREAM-II) was comprised of detectors based on different techniques (Cherenkov light, specific ionization in scintillators and silicon sensors) to provide a redundant charge identification and a thin ionization calorimeter capable of measuring the energy of cosmic rays up to several hundreds of TeV. The data analysis is described and the individual energy spectra of C, O, Ne, Mg, Si and Fe are reported up to ~ 10^14 eV. The spectral shape looks nearly the same for all the primary elements and can be expressed as a power law in energy E^{-2.66+/-0.04}. The nitrogen absolute intensity in the energy range 100-800 GeV/n is also measured.Comment: 4 pages, 3 figures, presented at ICRC 2009, Lodz, Polan

Measurements of cosmic-ray energy spectra with the 2nd CREAM flight

During its second Antarctic flight, the CREAM (Cosmic Ray Energetics And Mass) balloon experiment collected data for 28 days, measuring the charge and the energy of cosmic rays (CR) with a redundant system of particle identification and an imaging thin ionization calorimeter. Preliminary direct measurements of the absolute intensities of individual CR nuclei are reported in the elemental range from carbon to iron at very high energy.Comment: 4 pages, 3 figures, presented at XV International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2008

A new measurement of the altitude dependence of the atmospheric muon intensity

We present a new measurement of atmospheric muons made during an ascent of the High Energy Antimatter Telescope balloon experiment. The muon charge ratio mu+/mu- as a function of atmospheric depth in the momentum interval 0.3-0.9 GeV/c is presented. The differential mu- intensities in the 0.3-50 GeV/c range and for atmospheric depths between 4-960 g/cm^2 are also presented. We compare these results with other measurements and model predictions. We find that our charge ratio is ~1.1 for all atmospheric depths and is consistent, within errors, with other measurements and the model predictions. We find that our measured mu- intensities are also consistent with other measurements, and with the model predictions, except at shallow atmospheric depths.Comment: To appear in Physical Review

Energy spectra of cosmic-ray nuclei at high energies

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 $\sim 10^{14}$ eV. The spectral shape looks nearly the same for these primary elements and it can be fitted to an $E^{-2.66 \pm 0.04}$ 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 $0.080 \pm 0.025$(stat.)$\pm 0.025$(sys.) at $\sim$800 GeV/$n$, in good agreement with a recent result from the first CREAM flight.Comment: 32 pages, 10 figures. Accepted for publication in Astrophysical Journa

Cosmic-Ray Proton and Helium Spectra from the First CREAM Flight

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 $\pm$ 0.02 for protons from 2.5 TeV to 250 TeV and -2.58 $\pm$ 0.02 for helium nuclei from 630 GeV/nucleon to 63 TeV/nucleon. They are harder than previous measurements at a few tens of GeV/nucleon. 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 $\pm$ 0.5 for the range from 2.5 TeV/nucleon to 63 TeV/nucleon. This ratio is considerably smaller than the previous measurements at a few tens of GeV/nucleon.Comment: 20 pages, 4 figure

Measurement of the Cosmic-Ray Antiproton to Proton Abundance Ratio between 4 and 50 GeV

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 cut-off 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.Comment: 4 pages, 3 figures; accepted for publication in PR

The Composition of Cosmic Rays at the Knee

The observation of a small change in spectral slope, or 'knee' in the fluxes of cosmic rays near energies 10^15 eV has caused much speculation since its discovery over 40 years ago. The origin of this feature remains unknown. A small workshop to review some modern experimental measurements of this region was held at the Adler Planetarium in Chicago, USA in June 2000. This paper summarizes the results presented at this workshop and the discussion of their interpretation in the context of hadronic models of atmospheric airshowers.Comment: 36 pages, 10 figure