J. A. Bellido

Measurement of the flux of ultrahigh energy cosmic rays from monocular observations by the high resolution fly's eye experiment

We have measured the cosmic ray spectrum above 10^17.2 eV using the two air fluorescence detectors of the High Resolution Flys Eye observatory operating in monocular mode. We describe the detector, photo-tube and atmospheric calibrations, as well as the analysis techniques for the two detectors. We fit the spectrum to a model consisting of galactic and extra-galactic sources.

A Study of the Composition of Ultra-High-Energy Cosmic Rays Using the High-Resolution Fly’s Eye

The composition of Ultra High Energy Cosmic Rays (UHECR) is measured with the High Resolution Flys Eye cosmic ray observatory (HiRes) data using the Xmax technique. Data were collected in stereo between 1999 November and 2001 September. The data are reconstructed with well-determined geometry. Measurements of the atmospheric transmission are incorporated in the reconstruction. The detector resolution is found to be 30 g cm^-2 in Xmax and 13% in Energy. The Xmax elongation rate between 10^18.0 eV and 10^19.4 eV is measured to be 54.5 +/- 6.5 (stat) +/- 4.5 (sys) g cm^-2 per decade. This is compared to predictions using the QGSJet01 and SIBYLL 2.1 hadronic interaction models for both protons and iron nuclei. CORSIKA-generated Extensive Air Showers (EAS) are incorporated directly into a detailed detector Monte Carlo program. The elongation rate and the Xmax distribution widths are consistent with a constant or slowly changing and predominantly light composition. A simple model containing only protons and iron nuclei is compared to QGSJet and SIBYLL. The best agreement between the model and the data is at 80% protons for QGSJet and 60% protons for SIBYLL.The composition of ultra-high-energy cosmic rays is measured with the High Resolution Flys Eye cosmic-ray observatory data using the Xmax technique. Data were collected in stereo between 1999 November and 2001 September. The data are reconstructed with well-determined geometry. Measurements of the atmospheric transmission are incorporated in the reconstruction. The detector resolution is found to be 30 g cm-2 in Xmax and 13% in energy. The Xmax elongation rate between 1018.0 and 1019.4 eV is measured to be 54.5 ± 6.5 ± 4.5 g cm-2 per decade. This is compared with predictions using the QGSJet01 and SIBYLL 2.1 hadronic interaction models for both protons and iron nuclei. CORSIKA-generated extensive air showers are incorporated directly into a detailed detector Monte Carlo program. The elongation rate and the Xmax distribution widths are consistent with a constant or slowly changing and predominantly light composition. A simple model containing only protons and iron nuclei is compared with QGSJet and SIBYLL. The best agreement between the model and the data is for 80% protons for QGSJet and 60% protons for SIBYLL.

Southern hemisphere observations of a 1018 eV cosmic ray source near the direction of the Galactic Centre

We report on an analysis of data from the southern hemisphere SUGAR cosmic ray detector. We confirm the existence of an excess of 1018 eV cosmic rays from a direction close to the Galactic Centre, first reported by the AGASA group. We find that the signal is consistent with that from a point source, and we find no evidence for an excess of cosmic rays coming from the direction of the Galactic Centre itself.

Study of small-scale anisotropy of ultra-high-energy cosmic rays observed in stereo by the high resolution fly's eye detector

The High Resolution Flys Eye (HiRes) experiment is an air fluorescence detector which, operating in stereo mode, has a typical angular resolution of 0.6 degrees and is sensitive to cosmic rays with energies above 10^18 eV. HiRes is thus an excellent instrument for the study of the arrival directions of ultrahigh energy cosmic rays. We present the results of a search for anisotropies in the distribution of arrival directions on small scales (<5 degrees) and at the highest energies (>10^19 eV). The search is based on data recorded between 1999 December and 2004 January, with a total of 271 events above 10^19 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.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 .6 and is sensitive to cosmic rays with energies above 10 18 eV. The HiRes cosmic-ray detector is thus an excellent instrument for the study of the arrival directions of ultra–highenergy 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 (110 19 eV). The search is based on data recorded between 1999 December and 2004 January, with a total of 271 events above 10 19 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. Subject headings: acceleration of particles — cosmic rays — large-scale structure of universe

Search for point sources of ultra-high-energy cosmic rays above 4.0 × 1019 ev using a maximum likelihood ratio test

We present the results of a search for cosmic-ray point sources at energies in excess of 4.0 × 1019 eV in the combined data sets recorded by the Akeno Giant Air Shower Array and High Resolution Flys Eye stereo experiments. The analysis is based on a maximum likelihood ratio test using the probability density function for each event rather than requiring an a priori choice of a fixed angular bin size. No statistically significant clustering of events consistent with a point source is found.

Report of the Working Group on the Composition of Ultra High Energy Cosmic Rays

For the first time a proper comparison of the average depth of shower maximum (

A search for arrival direction clustering in the HiRes-I monocular data above 1019.5 eV

X_{\rm max}

Search for global dipole enhancements in the HiRes-I monocular data above 1018.5 eV

) published by the Pierre Auger and Telescope Array Observatories is presented. The

Geometry and optics calibration for air fluorescence detectors using star light

X_{\rm max}

The Prototype Opto-mechanical System for the Fluorescence detector Array of Single-pixel Telescopes

distributions measured by the Pierre Auger Observatory were fit using simulated events initiated by four primaries (proton, helium, nitrogen and iron). The primary abundances which best describe the Auger data were simulated through the Telescope Array (TA) Middle Drum (MD) fluorescence and surface detector array. The simulated events were analyzed by the TA Collaboration using the same procedure as applied to their data. The result is a simulated version of the Auger data as it would be observed by TA. This analysis allows a direct comparison of the evolution of