A Cross Check of Atmospheric Attenuation for the High Resolution Fly’s Eye Astroparticle Experiment Chris Cannon Advisor: Lawrence Wiencke University of Utah 1.Cosmic rays above 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 eV the flux is extremely low!!! Namely 1 particle/km 2 -steradian/century Flux E^3 Cosmic Ray Energy Spectrum Man-made accelerators

Using the Atmosphere as a Detector

Introducing High Resolution Fly’s Eye (HiRes)

Mirror PMT 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:

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 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 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 Luminosity (photons/m) Distance from Gound (m)

Plotting Data Difference in distance between detectors and shower Difference in shower brightness- 0 + Greater distance brighter shower. The atmosphere is over-corrected. Greater distance dimmer shower. The atmosphere is under-corrected.

Results Simulated Atmosphere Canonical Model Measured Average No Aerosols Comment Over-correction Under-correction

Conclusion: Using lasers Using cosmic rays (stat) VAOD Measurement

Effect of Atmospheric Calibration With Model Atmosphere With Measured Atmosphere

Greisen-Zatsepin-Kuzmin (GZK) Cutoff Charged particles with E > 5 x 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 Rays êThe Sun êSolar Wind êLow Energy < 10 GeV êSupernovae Capable of accelerating particles to eV êAGNs / GRBs … Possible sources for UHECRs

Requirements on acceleration size and field strength

Use Timing…. Depth Perception is Limited Need to measure a change in angular velocity Equal Angle Bins detector shower RpRp ψ Works best with Longer track Larger Rp Smaller ψ Geometry with One Eye