Fluorescence Yield of Cosmic Rays at Various Altitudes

Melissa May Maestas

Riverton High School

March 7, 2003

Cosmic Rays

Mostly charged particles from outer space

Two predominant components protons Iron nuclei

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Cosmic Ray Detector

Fluorescence light from particle shower can be detected by fast, sensitive cameras (“eyes”) on clear, moonless nightsSchematic of twin “eyes”

imaging an air shower

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HiRes

HiRes: High Resolution Fly’s Eye Group A collaboration of eight universities Mission: measure Ultra-High Energy Cosmic

Rays

Photons are detected with photo-multiplier tubes (PMTs)

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HiRes Detector

66 detector units each consisting of 2m diameter mirror and 256 PMTs

Each PMT views 1 degree cone of sky

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A 25 Microsecond Movie of An Air ShowerA 25 Microsecond Movie of An Air Shower

(playback at 1/500,000 speed)

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FLASH

FLASH: Fluorescence from Air in Showers Experiment to measure more precisely the

fluorescence yield Calibration of HiRes technique

Energy measured from amount of light detected

Beam pulses of ~billion electrons sent through chamber of gas

– Various pressures– PMT signal measured

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Stanford Linear Accelerator Center2-mile accelerator3x1010 eV electrons in pulses of

~109 particlesSite of FLASH experiment

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Chamber

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Experiment

Experiment involved 30 people including two month preparation period between April-June, 2002

Data collected during 3 week “run” in June, 2002 at SLAC

Additional calibration analysis still in progress to this date

My part in this effort included PMT calibration, data analysis and preparation for next FLASH run

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Experiment / Hypothesis

FLASH experiment simulated particle showers from cosmic rays

Hypothesis: Fluorescence yield would: Increase as pressure increases Decrease as altitude increases

Shower particles/electrons likely to interact more if more molecules present

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Analysis Procedure

Data selections made for pressure dependence analysis

Plotted: Full pressure range to find settings used Each pressure distribution to find its mean Digitized PMT signal at each pressure Mean PMT signals vs. mean pressures

Converted pressure to altitude P(z)=Poe-mgz/KT

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Pressure - Torr

Number of electron pulses

Pressure

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Number of electron pulses

Lowest Pressure Range

Pressure - Torr 16

Signal at Lowest Pressure Range

PMT Signal - ADC Counts

Number of electron pulses

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Discussion

Result: Yield increases at low pressures but levels off at higher pressures

Hypothesis supported at low pressures Higher yield - more molecules per unit length for

shower particles/electrons to interact with

Hypothesis not supported at higher pressures Maybe: At low pressures, only amount of gas

affects signal Maybe: At higher pressures, gas molecules interact

with each other, interfering with electrons

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Future Improvements & Experiments

Convert ADC counts to number of photons per electron

– Calibration project currently underway

Examine Various Beam charge ranges Higher beam charge - higher yield, same

relationship?? Part 2 of FLASH: Summer of 2003

wavelength dependence shower depth dependence

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Acknowledgments

Dr. Charles Jui Dr. John N. Matthews Dr. Petra Huentemeyer John Hinton Justin Findlay Cigdem Ozkan The HiRes Collaboration

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