Spectrum, Composition, and Arrival Direction of Ultra High Energy Cosmic Rays as Measured by HiRes

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Spectrum, Composition, and Arrival Direction of
Ultra High Energy Cosmic Rays as Measured by HiRes

• John Belz
• for the High Resolution Flys Eye

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The High Resolution Flys Eye (HiRes)
University of Adelaide Columbia University Los
Alamos National Lab University of
Montana University of New Mexico Rutgers
University University of Tokyo University of
Utah and IHEP (Beijing)
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Introduction Cosmic Rays over a Wide Energy Range

• Knee at 1015.5 eV is only feature over many
  decades
• Things get interesting at higher energies (gt1017
  eV.)
• Change from galactic to extragalactic sources.
• Expect features due to interactions between CR
  protons and CMBR photons.
• Learn about extragalactic sources and
  propagation over cosmic distances.

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Introduction HiRes

• HiRes is a two-eyed nitrogen fluorescence
  experiment studying UHE cosmic rays.
• Monocular Wide energy range (1017.4 lt E lt
  1020.5 eV), best statistics.
  
• Stereo best reconstruction, covers 1018.5 lt E lt
  1020.5 eV.
• Located at the armys Dugway Proving Grounds,UT.
• Two detectors, 13 km apart

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The HiRes Observatory at Camels Back Ridge
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Monocular Data Analysis

• Pattern recognition.
• Find SPD.
• Time fit (HiRes2)
• 5o resolution.
• Profile Plot
• Gaisser-Hillas fit.
• Profile-constrained fit (HiRes1), 7o resolution.

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Stereo Analysis

• Intersection of shower-detector planes determines
  geometry, 0.60 resolution.
• Timing does as well for parallel SDPs.
• Two measurements of energy, Xmax. Allows
  measurement of resolution.

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HiRes1 Energy Reconstruction

• Test HiRes1 PCF energy reconstruction using
  events seen in stereo.
• Reconstructed energy using mono PCF geometry vs.
  energy using stereo geometry.
• Get same answer.

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Aperture Calculation Data/Monte Carlo
Comparisons

• Monte Carlo Input
• Flys Eye stereo spectrum
• HiRes/Mia composition
• Library of Corsika showers
• Nightly detector information

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Data / Monte Carlo Comparisons
Result excellent simulation of the data. ?
Credible spectral calculation
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Monocular Spectra
HiRes1 7/97-2/03 Hi/res2 12/99-9/01
We observe ankle GZK
suppression at correct energy
second knee?
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Two SpectraHiRes Mono and Flys Eye Stereo

• Flys Eye stereo spectrum shows second knee at
  1017.6 eV.
• HiRes cannot claim observation of second knee.

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Does the Spectrum Continue Unabated as a Power
Law?

• Fit from ankle to pion production threshold
• Extend beyond
• Expect 29.0 events, see 11
• Poisson probability 1x10-4
• Suppression is significant.
• ?We have good sensitivity, but the
  events are not there.

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Monocular Spectrum Comparison with AGASA

• Two discrepancies
• Energy scale shift
• Disagreement on continuation beyond
  pion-production threshold

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SLAC E-165 FLuorescence in Air Showers SLAC,
Utah, Montana, Rutgers, COSPA

• Thin Target Measure absolute air fluorescence
  yield as function of
• Wavelength
• Pressure
• Atmospheric Composition
• Thick Target (Summer 2004) Probe dependence on
  charged particle energy. Compare light yield to
  dE/dT

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Stereo Spectrum
Stereo black HiRes1 mono red HiRes2 mono blue
In agreement with mono, But poorer statistics.
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Composition

• Stereo measurement of Xmax vs. energy
• Elongation rate changes from 90 to 50
  g/cm2/decade at 1018.0 eV.
• Marks transition from galactic to extragalactic
  CRs.

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Anisotropy Searches

• HiRes-1 monocular anisotropy
• asymmetric error bars,
• 7 x 0.5

Stereo anisotropy tiny error bars 0.5 x
0.5
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Large Scale Anisotropy Search Dipole
Enhancement(suggested by Biermann et al., and
Farrar et al.)
Source Location a Galactic Center
.01 .05 Centaurus A -.02
.06 M87 -.02
.03 Astropart. Phys. 21 (2004)
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Anisotropy above 1018.5 eV Search for Pointlike
Sources
Significance Map HiRes Monocular Data
Significance Map Simulated 25-event Point Source
Exclude sources gt 0.6 events/km2yr (90 c.l.)
(to be submitted to Astropart. Phys.)
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Anisotropy Searches Autocorrelation
HiRes
Agasa

• HiRes1 Monocular
• None seen.
• astro-ph/0404366
• Stereo scan in energy and angle.
• None found most significant point has
  Pchance.52
• Ap. J. 610 (2004)

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Comparison with AGASA Cluster Results

• Promote the 6 AGASA clusters to be sources of UHE
  cosmic rays.
• Allowing for energy scale shifts find 6 overlaps
  at 3s expect 6.6 randomly
• Joint probability is 0.001
• ?The 6 AGASA clusters are NOT sources of
  constant intensity.
• Caveat if 2 AGASA clusters are of random
  origin, then joint probability is 0.01
• To be submitted to Ap. J. Lett.

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Summary HiRes Physics Results

• HiRes Spectra
• See two (of the three) spectral features
• Two caused by CR CMBR interactions
• Stereo spectrum agrees, more statistics needed.
• Stereo Composition Measurement
• Composition is light from 1018 to 1019.4
• Change in elongation at about 1018 eV.
• Anisotropy Searches
• Null results at all angular scales cosmic ray
  astronomy still in its infancy!
• Inconsistent with AGASA clustering claims

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The Ultimate UHECR Experiment

• Wed like to see all three spectral features with
  single experiment
• Second Knee
• Ankle e e- production
• GZK supression
• Observe the galactic/extragalactic transition via
  composition change
• Find where these things are coming from
  Anisotropy studies
• Characteristics
• Wide energy coverage 1017.0 to 1020.5 eV
• Excellent spectral resolution need fluorescence.
• Composition Seeing Xmax is very important
  again need fluorescence.
• A large ground array is necessary
• Ground array great for anisotropy above 1019 eV.

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Ultimate (continued)Telescope Array (TA)/TALE

• Large ground array.
• Powerful fluorescence detector
• TA and HiRes fluorescence detectors combined.
• Fluorescence aperture gt Ground array aperture.
• Energy range from below 1017.0 to 1020.5 eV.
• Higher elevation angle coverage lower energy
  threshold.
• Infill array for improved low energy
  measurements.
• Excellent site Millard Co. Utah has mountains
  for fluorescence detectors, flat valley floor for
  ground array.
• Good atmosphere, detectors above the aerosol
  muck.
• Accomplish all the goals in previous slide.