Study of Small-Scale Anisotropy of Ultra-High-Energy Cosmic Rays Observed in Stereo by the High Resolution Fly’s Eye Detector

R. U. Abbasi; T. Abu-Zayyad; J. F. Amann; G. Archbold; R. Atkins; J. A. Bellido; K. Belov; J. W. Belz; S. BenZvi; D. R. Bergman; J. H. Boyer; G. W. Burt; Z. Cao; R. W. Clay; B. M. Connolly; B. R. Dawson; W. Deng; Y. Fedorova; J. Findlay; C. B. Finley; W. F. Hanlon; C. M. Hoffman; M. H. Holzscheiter; G. A. Hughes; P. Hüntemeyer; C. C. H. Jui; K. Kim; M. A. Kirn; B. C. Knapp; E. C. Loh; M. M. Maestas; N. Manago; E. J. Mannel; L. J. Marek; K. Martens; J. A. J. Matthews; J. N. Matthews; A. O’Neill; C. A. Painter; L. Perera; K. Reil; R. Riehle; M. D. Roberts; M. Sasaki; S. R. Schnetzer; M. Seman; K. M. Simpson; G. Sinnis; J. D. Smith; R. Snow; P. Sokolsky; C. Song; R. W. Springer; B. T. Stokes; J. R. Thomas; S. B. Thomas; G. B. Thomson; D. Tupa; S. Westerhoff; L. R. Wiencke; A. Zech; (The HiRes Collaboration)

doi:10.1086/423303

Study of Small-Scale Anisotropy of Ultra-High-Energy Cosmic Rays Observed in Stereo by the High Resolution Fly's Eye Detector

R. U. Abbasi¹, T. Abu-Zayyad¹, J. F. Amann², G. Archbold¹, R. Atkins¹, J. A. Bellido³, K. Belov¹, J. W. Belz⁴, S. BenZvi⁵, D. R. Bergman⁶, J. H. Boyer⁵, G. W. Burt¹, Z. Cao¹, R. W. Clay³, B. M. Connolly⁵, B. R. Dawson³, W. Deng¹, Y. Fedorova¹, J. Findlay¹, C. B. Finley⁵, W. F. Hanlon¹, C. M. Hoffman², M. H. Holzscheiter², G. A. Hughes⁶, P. Hüntemeyer¹, C. C. H. Jui¹, K. Kim¹, M. A. Kirn⁴, B. C. Knapp⁵, E. C. Loh¹, M. M. Maestas¹, N. Manago⁷, E. J. Mannel⁵, L. J. Marek², K. Martens¹, J. A. J. Matthews⁸, J. N. Matthews¹, A. O'Neill⁵, C. A. Painter², L. Perera⁶, K. Reil¹, R. Riehle¹, M. D. Roberts⁸, M. Sasaki⁷, S. R. Schnetzer⁶, M. Seman⁵, K. M. Simpson³, G. Sinnis², J. D. Smith¹, R. Snow¹, P. Sokolsky¹, C. Song⁵, R. W. Springer¹, B. T. Stokes¹, J. R. Thomas¹, S. B. Thomas¹, G. B. Thomson⁶, D. Tupa², S. Westerhoff⁵, L. R. Wiencke¹, A. Zech⁶, and (The HiRes Collaboration)

Published 2004 June 25 • © 2004. The American Astronomical Society. All rights reserved. Printed in U.S.A.
The Astrophysical Journal, Volume 610, Number 2 Citation R. U. Abbasi et al 2004 ApJ 610 L73 DOI 10.1086/423303

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Author affiliations

¹ University of Utah, Department of Physics and High Energy Astrophysics Institute, Salt Lake City, UT 84112

² Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545

³ University of Adelaide, Department of Physics, Adelaide, SA 5005, Australia

⁴ University of Montana, Department of Physics and Astronomy, Missoula, MT 59812

⁵ Columbia University, Department of Physics and Nevis Laboratories, New York, NY 10027

⁶ Rutgers, The State University of New Jersey, Department of Physics and Astronomy, 136 Frelinghuysen Road, Piscataway, NJ 08854-8019

⁷ University of Tokyo, Institute for Cosmic Ray Research, 515 Kashiwa-no-Ha, Kashiwa City, Chiba 277-8582, Japan

⁸ University of New Mexico, Department of Physics and Astronomy, Albuquerque, NM 87131

Dates

Received 2004 April 6
Accepted 2004 June 14
Published 2004 June 25

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Abstract

The High Resolution Fly's Eye (HiRes) experiment is an air fluorescence detector which, operating in stereo mode, has a typical angular resolution of 0 fdg 6 and is sensitive to cosmic rays with energies above 10¹⁸ eV. The HiRes cosmic-ray detector is thus an excellent instrument for the study of the arrival directions of ultra-high-energy cosmic rays. We present the results of a search for anisotropies in the distribution of arrival directions on small scales (<5°) and at the highest energies (>10¹⁹ eV). The search is based on data recorded between 1999 December and 2004 January, with a total of 271 events above 10¹⁹ eV. No small-scale anisotropy is found, and the strongest clustering found in the HiRes stereo data is consistent at the 52% level with the null hypothesis of isotropically distributed arrival directions.

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