K. Martens

First observation of the Greisen-Zatsepin-Kuzmin suppression.

The High Resolution Flys Eye (HiRes) experiment has observed the Greisen-Zatsepin-Kuzmin suppression (called the GZK cutoff) with a statistical significance of five standard deviations. HiRes measurement of the flux of ultrahigh energy (UHE) cosmic rays shows a sharp suppression at an energy of

Indications of Proton-Dominated Cosmic-Ray Composition above 1.6 EeV

6 times 10^{19}

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

eV, consistent with the expected cutoff energy. We observe the ``ankle of the cosmic-ray energy spectrum as well, at an energy of

Search for correlations between HiRes stereo events and active galactic nuclei

4 times 10^{18}

Search for cross-correlations of ultrahigh-energy cosmic rays with BL Lacertae objects

eV. We describe the experiment, data collection, analysis, and estimate the systematic uncertainties. The results are presented and the calculation of the statistical significance of our observation is described.

Measurement of the flux of ultra high energy cosmic rays by the stereo technique

We report studies of ultrahigh-energy cosmic-ray composition via analysis of depth of air shower maximum (X(max)), for air shower events collected by the High-Resolution Flys Eye (HiRes) observatory. The HiRes data are consistent with a constant elongation rate d/d[log(E)] of 47.9+/-6.0(stat)+/-3.2(syst) g/cm2/decade for energies between 1.6 and 63 EeV, and are consistent with a predominantly protonic composition of cosmic rays when interpreted via the QGSJET01 and QGSJET-II high-energy hadronic interaction models. These measurements constrain models in which the galactic-to-extragalactic transition is the cause of the energy spectrum ankle at 4x10(18) eV.

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

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.

ANALYSIS OF LARGE-SCALE ANISOTROPY OF ULTRA-HIGH ENERGY COSMIC RAYS IN HiRes DATA

Abstract We have searched for correlations between the pointing directions of ultrahigh energy cosmic rays observed by the High Resolution Fly’s Eye experiment and active galactic nuclei (AGN) visible from its northern hemisphere location. No correlations, other than random correlations, have been found. We report our results using search parameters prescribed by the Pierre Auger collaboration. Using these parameters, the Auger collaboration concludes that a positive correlation exists for sources visible to their southern hemisphere location. We also describe results using two methods for determining the chance probability of correlations: one in which a hypothesis is formed from scanning one half of the data and tested on the second half, and another which involves a scan over the entire data set. The most significant correlation found occurred with a chance probability of 24%.

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

Data taken in stereo mode by the High Resolution Flys Eye (HiRes) air fluorescence experiment are analyzed to search for correlations between the arrival directions of ultra--high-energy cosmic rays with the positions of BL Lacertae objects. Several previous claims of significant correlations between BL Lacs and cosmic rays observed by other experiments are tested. These claims are not supported by the HiRes data. However, we verify a recent analysis of correlations between HiRes events and a subset of confirmed BL Lacs from the 10th Veron Catalog, and we study this correlation in detail. Due to the a posteriori nature of the search, the significance level cannot be reliably estimated and the correlation must be tested independently before any claim can be made. We identify the precise hypotheses that will be tested with statistically independent data.Data taken in stereo mode by the High Resolution Flys Eye (HiRes) air fluorescence experiment are analyzed to search for correlations between the arrival directions of ultrahigh-energy cosmic rays with the positions of BL Lacertae objects. Several previous claims of significant correlations between BL Lac objects and cosmic rays observed by other experiments are tested. These claims are not supported by the HiRes data. However, we verify a recent analysis of correlations between HiRes events and a subset of confirmed BL Lac objects from the 10th Veron Catalog, and we study this correlation in detail. Due to the a posteriori nature of the search, the significance level cannot be reliably estimated and the correlation must be tested independently before any claim can be made. We identify the precise hypotheses that will be tested with statistically independent data.

Measurement of Pressure Dependent Fluorescence Yield of Air: Calibration Factor for UHECR Detectors

The High Resolution Fly’s Eye (HiRes) experiment has measured the flux of ultrahigh energy cosmic rays using the stereoscopic air fluorescence technique. The HiRes experiment consists of two detectors that observe cosmic ray showers via the fluorescence light they emit. HiRes data can be analyzed in monocular mode, where each detector is treated separately, or in stereoscopic mode where they are considered together. Using the monocular mode the HiRes collaboration measured the cosmic ray spectrum and made the first observation of the Greisen–Zatsepin–Kuzmin cutoff. In this paper we present the cosmic ray spectrum measured by the stereoscopic technique. Good agreement is found with the monocular spectrum in all details.