Ultra-High Energy Cosmic Ray Research with the Pierre Auger Observatory

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Ultra-High Energy Cosmic Ray Research with the
Pierre Auger Observatory

• Methods, Results, What We Learn,
• and expansion to Colorado
• Bill Robinson

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Mysteries of Ultra-High Energy Cosmic Rays

• What are they made of through the range of
  energies?
• What accelerates them?
• How energetic can they get?
• Why do we detect UHECRs that are too energetic to
  be allowed by current theory?
• Where do they come from? And why do different
  detectors get different results?

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(S. Swordy, AUGER design report)
power law E-2.8 Above knee supernova remnant
shocks Below knee where from? Upper limit GZK
cutoff at ankle, most energetic yet 3 E 20 eV or
300 EeV 1 EeV 10 E18, Exaelectron Volt
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(from http//www.mpi-hd.mpg.de/hfm/CosmicRay/Showe
rs.html)
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Simulated Longitudinal development of 50 1 EeV
Cascades
M. Ambrosio et. al., Astroparticle Physics 24,
355-371 (2005).
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Interaction Depth of shower maximum (PAO 850
g/cm2 sea level 1000 interstellar space
108 LY)
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1 EeV Anisotropy from Akeno
Ratio of of observed events to expected ones in
equatorial coordinate. Solid line Galactic
Plane, G.C. is galactic center. Amplitude 4
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Galactic region of excess (Akeno)
Ion gyroradius cgs
m mass in proton units Z ionization E
energy in eV Galactic B 3 microgauss R for 1
EeV proton 300 pc
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Anisotropies in HE Arrival Direction
From the Japanese Akeno observatory, above 40
EeV, 19902002
But theres a lot of controversy about this..
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Problems

• Shaded circles show clustering within 2.5
  degrees chance probability of 0.9 for just one
  triple event
• BUT this is not corroborated by other
  observatories when they show anisotropies they
  are in other directions
• No sources in arrival directions away from
  galaxy
• Neutrons of 10 EeV have gamma 10 E9, so a range
  of about 10 kpc galactic center within range.
  Immune to field deflections. No anisotropies
  below 10 E17.9
• Impossible to detect directly if neutrons are
  primaries
• Only Akeno shows galactic center and Cygnus
  clustering
• Extremely low flux and contradictory results are
  good arguments for more observatories using
  multiple detection methods in different regions
• Have to separate gamma ray showers from nuclei

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PAO fails to find excess
10 E17.9 lt E lt 10 E 18.5, 5 degree windows, GC at
cross, line is galactic plane 2.3 years of Auger
data, no abnormally over-dense regions, cannot
resolve probable source at GC (must use gamma
rays to investigate)
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GZK Cutoff? (2003, pre-PAO)
arXivhep-ph/o206217 v5 27 Feb 2003, Has the GZK
suppression been discovered?
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PAO (south) near completion
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PAO Hybrid Detector
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Lonesome Water Tank and the Andes
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Fluorescence telescope enclosure
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UHECR Energy loss and calibration
Energy loss in the shower

• with Nem particle density along shower
  direction x, Nph photons reaching fluorescence
  detector, R(x) distance from shower point x and
  FD, T(x) atmospheric transmission (lt1)

Energy loss in the shower
Energy loss in the shower
Night atmosphere assumed horizontally Invariant
only steered through zenith angle, probes to 30
km tracing losses to molecular and aerosol
scattering. Requires clear moonless nights 14
duty cycle.
Calibration with Lidar
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Auger fluorescence telescope
Diameter 2.2 meters Aperture 3.8 sq. m. 440
photomultiplier tubes Schematic shows positions
of diffusers for optical calibrations
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Central Laser Facility (PAO South)

• UV laser (355 nm) fires 7 ns, 7 mJ pulse every 15
  minutes to calibrate FDs scattered luminosity
  approx. same as strong shower
• Located equidistant from 3 of the 4 FD eyes
• Polarization randomized (better than circular)
• Can fire in any direction
• Weather checked by instruments every 5 minutes

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PAO proposed initial Colorado site
(Middle of Nowhere)
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Conclusion

• More detectors needed!
• Colorado site ideal funding on order of 100
  million room for huge expansion
• Primary questions remain unresolved
• Existing PAO works both physically and
  politically as a model of international
  cooperation

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References

• Websites
• History of the Air Fluorescence Technique,
• www.cosmic-ray.org/reading/fluor.html
• Pierre Auger Observatory www.auger.org and
  www.augernorth.org
• AGASA www-akeno.icrr.u-tokyo.ac.jp/AGASA/
• Interaction Depth www.lbl.gov/abc/cosmic/SKliewer/
  Cosmic_Rays/Interaction.htm
• Journals
• M. Ambrosio et. al., Astroparticle Physics 24,
  355-371 (2005).
• Pierre Auger Collaboration, arXivastro-ph 3,
  0607382 (2006).
• N. Hayashitda et al., Astroparticle Physics 10,
  310 (1999).
• J. Bahcall and Eli Waxman, arXivhep-ph 5,
  0206217 (27 Feb 2003).
• A. Filipcic et. al., Astroparticle Physics 18,
  502 (2003).
• Optical Relative Calibration for Auger
  Fluorescence Detector, and Performance of the PAO
  Surface Array, Pune (2005) 00, 101-106
• The Central Laser Facility at the PAO, Subm. To
  Nucl. Inst. Meth. 06