A Cross Check of Atmospheric Attenuation for the High Resolution Fly’s Eye Astroparticle...
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A Cross Check of Atmospheric Attenuation for the High Resolution Fly’s Eye Astroparticle Experiment
Chris CannonAdvisor: 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
At energies above 1020 eV the flux is extremely low!!!Namely 1 particle/km2-steradian/century
Flux
E^3
Cosmic Ray Energy SpectrumCosmic Ray Energy Spectrum
Man-made accelerators
Using the Atmosphere as a Detector
Introducing High Resolution Fly’s Eye (HiRes)
MirrorPMT Cluster
HiRes Camera
Display of a Sample Air Shower
The Atmosphere – Two Components
Vertical Aerosol Optical Depth (VAOD) is the optical thickness of the aerosol component of the atmosphere.
Transmission(aerosol) = e-VAOD
Molecular Aerosols
Measuring VAOD with Atmospheric Lasers
HiRes-1 detector
HiRes-2 laser system
12.6 km
Average VAOD: 0.04 +- .02
Measuring VAOD with Cosmic Rays
Reality
Erroneous Simulation - Overcorretion
Erroneous Simulation - Undercorrection
detector 1
detector 2
apparent shower 1
apparent shower 2
apparent shower 1
apparent shower 2
Data SelectionStart 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.
Use the segment of the shower viewed by
both detectors.Profile integration
Lum
inos
ity (p
hoto
ns/m
)
Lum
inos
ity (p
hoto
ns/m
)
Distance from Gound (m) Distance from Gound (m)
Plotting Data
Difference in distance between detectors and shower
Diff
eren
ce in
show
er b
right
ness
- 0 +
-
0
+
Greater distance
brighter shower.
The atmosphere is over-corrected.
Greater distance dimmer shower.
The atmosphere is under-corrected.
ResultsSimulated Atmosphere
Canonical Model
Measured Average
No Aerosols
Comment
Over-correction
Under-correction
Conclusion:
Using lasers .04 +- .02Using cosmic rays .043 +- .001 (stat)
VAOD Measurement
Effect of Atmospheric Calibration
1999 2003
With Model Atmosphere With Measured Atmosphere
Greisen-Zatsepin-Kuzmin (GZK) Cutoff
Charged particles with E > 5 x 1019 eV will travel at most 100 Mpc before their energy drops below the cutoff.
HiRes Atmospheric Works in Progress• Improved atmospheric monitoring:
• Hourly aerosol corrections instead of average.
• Cloud monitoring.
Sources of Cosmic RaysSources of Cosmic Rays
The SunSolar WindLow Energy < 10 GeV
SupernovaeCapable of accelerating particles to 1015eV
AGNs / GRBs …Possible sources for UHECRs
Requirements on Requirements on acceleration size acceleration size and and field field strengthstrength
Use Timing…. Depth Perception is Limited
Need to measure a change in angular velocity
Equal Angle Bins
detector
shower
Rp
ψ
Works best withLonger trackLarger RpSmaller ψ
Geometry with One Eye