We describe the current status of the High Resolution Fly's Eye detector. Event reconstruction and associated systematics for stereo reconstruction are discussed and recent preliminary results on the study of the composition of ultra-high energy cosmic rays by the Xmax method are presented. These results indicate that the composition of cosmic rays becomes predominantly light near 1019 eV and beyond.
Lawrence Wiencke, Richard Gray, J. Reid Mumford, T. Abu-Zayyad, Y. Au, G. Archbold, K. Belov, J. Belz, D. Bergman, J. Boyer, Z. Cao, G. Chen, R. Clay, B. Dawson, B. Dieterle, B. Jones, C.C. Jui, D. Kieda, K. Kiyong, B. Knapp, W. Lee, Eugene Loh, E. Mannel, G. Martin, John Matthews, Joseph Meyer, K. Reil, J. Smith, Pierre Sokolsky, C. Song, W. Springer, Shanshan Taylor, Stan Thomas, T. Vanderveen, X. Zhang
Monitoring the aerosol component of the lowest 10 km of the atmosphere at UV wavelengths (300 - 400 nm) is an important part of the High Resolution Fly's Eye astrophysics experiment. Our method of atmospheric monitoring uses a frequency tripled YAG laser and a steering system that can point the beam anywhere in the sky. The same detector that measures scintillation light from high energy cosmic rays also measures light scattered from this laser system over a range of laser energies, geometries, and polarizations. This paper describes the technique, the laser system, and some recent measurements.
Lawrence Wiencke, D. Bird, G. Chen, R. Clay, H. Dai, B. Dawson, M. Huang, C.C. Jui, M. Kidd, D. Kieda, S. Ko, C. Larsen, Eugene Loh, J. Smith, Pierre Sokolsky, Paul Sommers, J. Tang, Stan Thomas, C. Wilkinson, S. Yoshida
The High Resolution Fly's Eye (HiRes) cosmic ray detector at Dugway Utah, measures UV scintillation light from extensive air showers. The detection technique is calorimetric in that the amount of light produced is proportional to the energy of the primary particle. Primary particle energies range from 1017 to more than 1020 electron volts. The detector can measure air showers more than 30 km away, a distance of several atmospheric extinction lengths. Variations in the atmosphere can cause significant variations in the amount of light reaching the detector. Atmospheric monitoring is extremely important. This paper discusses a method, under development, that uses the HiRes detector to measure light scattered from pulsed collimated xenon flashbulb sources (Flashers). Discussion includes a description of the light sources and a preliminary data analysis to extract a measurement of atmospheric extinction length and scale height.
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