Cosmic ray energy spectrum measurement with the Antarctic Muon and Neutrino Detector Array (AMANDA).

摘要

AMANDA-II is a neutrino telescope composed of 677 optical sensors organized along 19 strings buried deep in the Antarctic ice cap. It is designed to detect Cherenkov light produced by cosmic-ray- and neutrino-induced charged leptons. The majority of events recorded by AMANDA-II are caused by muons which are produced in the atmosphere by high-energy cosmic rays. The leading uncertainties in simulating such events come from the choice of the high-energy model used to describe the first interaction of the cosmic rays, uncertainties in our knowledge and implementation of the ice properties at the depth of the detector, and individual optical module sensitivities. Contributions from uncertainties in the atmospheric conditions and muon cross sections in ice are smaller.; The downgoing muon simulation was substantially improved by using the extensive air shower generator CORSIKA to describe the shower development in the atmosphere, and by writing a new software package for the muon propagation (MMC), which reduced computational and algorithm errors below the level of uncertainties of the muon cross sections in ice.; A method was developed that resulted in a flux measurement of cosmic rays with energies 1.5--200 TeV per nucleon (95% of primaries causing low-multiplicity events in AMANDA-II have energies in this range) independent of ice model and optical module sensitivities. Predictions of six commonly used high-energy interaction models (QGSJET, VENUS, NEXUS, DPMJET, HDPM, and SIBYLL) are compared to data. The best agreement with direct measurements is achieved with QGSJET, VENUS, and NEXUS. Assuming a power-law energy spectrum (phi0,i · E -gammai) for cosmic-ray components from hydrogen to iron (i = H,..., Fe) and their mass distribution according to Wiebel-South (Wiebel-South & Biermann, 1999), phi 0,i and gammai were corrected to achieve the best description of the data. For the hydrogen component, values of phi0,H = 0.106 +/- 0.007 m-2 sr-1s-1TeV-1 , gammaH = 2.70 +/- 0.02 are obtained. For the South Pole, a vertical muon flux at 1 TeV of (1.05 +/- 0.07) · 10 -10 cm-2 sr-1s -1GeV-1 is obtained (for all interaction models), and the fitted spectral index is 2.66 +/- 0.02 (for QGSJET, VENUS, and NEXUS). The difference in the predicted value of the spectral index gamma between high-energy interaction models is as much as 0.1, which is explained by the difference in the observed muon multiplicity at the depth of the detector in data simulated with different interaction models.