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