J. W. Elbert

HiRes, a High Resolution Fly's Eye detector

Abstract The High Resolution Eye detector (HiRes), based on the Flys Eye technique [1], is being developed at Dugway, Utah. Detector parameters and some preliminary test results will be given.

Mapping the U.H.E. sky in search of point sources

Abstract Techniques are presented for mapping the sky to search for density excesses attributable to point sources. By incorporating event-by-event angular resolution information, a scatter plot of arrival directions becomes the map of a smooth density function. Methods are discussed for quantitatively comparing that observed density function with the expected density function and evaluating the statistical significance of density excesses. Analysis of Flys Eye data provides examples of the techniques.

Limits on the ≳1017 eV cosmic ray νe flux

We report on a search for upward‐going extensive aire showers using the University of Utah Fly’s Eye detector. No event have been found in 6×106s of running time. The resultant νe flux limit for σν=10−33 cm2 varies from 7.2×10−14 to 5.0×10−17 ν/cm2‐sec‐ster for Eν between 1018 and 1021 eV. We also present limits for larger σν using near‐horizontal events originating in the atmosphere.

Measurement of cosmic ray air shower development at energies above 1017eV

Abstract We present measurements of the depth of maximum for extensive air showers (EAS) produced by cosmic ray nuclei with energies above 10 17 eV. The air showers were observed using the University of Utahs Flys Eye detectors operating in stereo mode. Measurements of the atmospheric nitrogen fluorescence light generated by EAS have been used to obtain longitudinal development curves of individual showers and, in particular, the depth of maximum of each shower. The data imply an elongation rate of 89 ± 6 g cm −2 per decade above 10 17 eV. The distribution of depths of shower maximum has a mean value of 690 ± 3 g cm −2 (with an estimated systematic uncertainty of ± 20 g cm −2 ) and a width (standard deviation) of 85 ± 2 g cm −2 for showers with energies above 3 × 10 17 eV. The tail of the distribution has a logarithmic decrement of λ = 70 ± 14 g cm −2 . Comparisons with predictions for a pure proton and a pure iron flux indicate that the data are not consistent with either.

Preliminary fly’s eye results

We describe a unique experiment, the Fly’s Eye, designed to measure extensive air showers (EAS) in the energy range 1017–1021 eV via atmospheric fluorescence. Preliminary results are presented for the following measurements: (1) limits on the extragalactic neutrino flux at 1020 eV, (2) the high energy cosmic ray spectrum, (3) Sources of high energy cosmic rays, (4) the total proton cross section σpp.

Results from the fly’s eye experiment

We report recently analyzed results on the energy spectrum, and composition of cosmic rays above 0.3 EeV. We observe a break in the spectrum at 3 EeV and a changing composition. The results can be explained by a simple two component model: galactic cosmic rays dominated by heavy primaries and an extragalactic component dominated by light primaries. The observed isotropic arrival direction distribution is consistent with the predictions of this model. A 320 EeV event was also recorded.

Recent Results from the Fly’s Eye Experiment

We report on recent results from the Fly’s Eye experiment up to July 1992. The detector consists of FE1, running from 1981 to 1992, and FE2 running from 1986 till now. The monocular data comes from a single eye detector, and the stereo data are detected by both detectors and reconstructed by stereo geometry. This report includes results on the spectrum, composition, anisotropy, and a 320 EeV event. The stereo spectrum shows a dip around 1018.5eV. The composition changes from predominately heavy (below 1018eV) to predominately light (above 1019eV). The anisotropy shows no significant deviation from random fluctuation in both a small scale and large scale anisotropy search. A 320 -40 +35 × 1018eV event was detected by FE1 on Oct. 15, 1991.

Evidence for Emission of Neutral Particles from Cygnus X-3 With Energy Greater Then 3x105 TeV

We report on preliminary results from a cosmic ray anisotropy search using the Fly’s Eye detector.[1] This detector records scintillation light emitted by extensive air showers in the atmosphere. The threshold for observing such showers with good efficiency and long-term stability is 3x105 TeV. Information available from the measurement includes the zenith and azimuthal angles, the impact parameter of the incident particle to the detector, the total energy, and the position of the shower maximum Xmax in the atmosphere.