A Cross Check of Atmospheric Attenuation for the High Resolution Fly

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A Cross Check of Atmospheric Attenuation for the
High Resolution Flys Eye Astroparticle
Experiment Chris Cannon Advisor Lawrence
Wiencke University of Utah

1. Cosmic rays above 1017 eV the highest energy
   particles
2. Atmospheric attenuation plays a significant role
   in detector calibration.
3. Cross check atmospheric calibration
4. Results
5. Conclusion

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Cosmic Ray Energy Spectrum
Flux E3
Man-made accelerators
At energies above 1020 eV the flux is extremely
low!!! Namely 1 particle/km2-steradian/century
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Using the Atmosphere as a Detector
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Introducing High Resolution Flys Eye (HiRes)
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HiRes Camera
Mirror
PMT Cluster
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Display of a Sample Air Shower
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The Atmosphere Two Components
Aerosols
Molecular

• Vertical Aerosol Optical Depth (VAOD) is the
  optical thickness of the aerosol component of the
  atmosphere.
• Transmission(aerosol) e-VAOD

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Measuring VAOD with Atmospheric Lasers
Average VAOD 0.04 - .02
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Measuring VAOD with Cosmic Rays
detector 2
Reality
detector 1
Erroneous Simulation - Overcorretion
apparent shower 2
apparent shower 1
apparent shower 2
Erroneous Simulation - Undercorrection
apparent shower 1
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Data Selection

• Start with 2079 cosmic rays seen by both
  detectors.
• Require that
• The two detectors see a common portion of the
  shower.
• Each detector must collect at least 1000 photons
  from the common track segment, which must be at
  least 5 degrees long.
• The probability that the event is noise based on
  a random walk model is less than 5.
• The event is downward going.
• The opening angle between shower-detector planes
  is greater than 25 degrees.
• The scattering angle is at least 25 degrees.
• 1218 cosmic ray events remain.

Purpose of Cuts Remove noisy, dim
events. Ensure good geometry. Remove Cherenkov
dominated events.
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Use the segment of the shower viewed by both
detectors.
Profile integration
Luminosity (photons/m)
Luminosity (photons/m)
Distance from Gound (m)
Distance from Gound (m)
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Plotting Data
Greater distance brighter shower. The
atmosphere is over-corrected.
Difference in shower brightness
- 0
Greater distance dimmer shower. The
atmosphere is under-corrected.
- 0
Difference in distance between detectors and
shower
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Results
Simulated Atmosphere Canonical Model Measured
Average No Aerosols
Comment Over-correction Under-correction
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Conclusion
VAOD Measurement
Using cosmic rays .043 - .001 (stat)
Using lasers .04 - .02
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Effect of Atmospheric Calibration
1999
2003
With Model Atmosphere
With Measured Atmosphere
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Greisen-Zatsepin-Kuzmin (GZK) Cutoff

• Charged particles with E gt 5 x 1019 eV will
  travel at most 100 Mpc before their energy drops
  below the cutoff.

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HiRes Atmospheric Works in Progress

• Improved atmospheric monitoring
• Hourly aerosol corrections instead of average.
• Cloud monitoring.

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Sources of Cosmic Rays

• The Sun
• Solar Wind
• Low Energy lt 10 GeV
• Supernovae
• Capable of accelerating particles to 1015eV
• AGNs / GRBs
• Possible sources for UHECRs

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Requirements on acceleration size and field
strength
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Geometry with One Eye
Use Timing. Depth Perception is Limited Need to
measure a change in angular velocity
Works best with Longer track Larger Rp Smaller ?