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Dissertation Calibration of the Pierre Auger Observatory Fluorescence Detectors and the Effect on Measurements Submitted by Ben Gookin Department of Physics In partial fulfillment of the requirements For the Degree of Doctor of Philosophy Colorado State University Fort Collins, Colorado Summer 2015 Doctoral Committee: Advisor: John Harton Walter Toki Kristen Buchanan Carmen Menoni Copyright by Ben Gookin 2015 All Rights Reserved Abstract Calibration of the Pierre Auger Observatory Fluorescence Detectors and the Effect on Measurements The Pierre Auger Observatory is a high-energy cosmic ray observatory located in Malarg¨ue, Mendoza, Argentina. It is used to probe the highest energy particles in the Universe, with energies greater than 1018 eV, which strike the Earth constantly. The observatory uses two techniques to observe the air shower initiated by a cosmic ray: a surface detector composed of an array of more than 1600 water Cherenkov tanks covering 3000 km2, and 27 nitrogen fluorescence telescopes overlooking this array. The Cherenkov detectors run all the time and therefore have high statistics on the air showers. The fluorescence detectors run only on clear moonless nights, but observe the longitudinal development of the air shower and make a calorimetric measure of its energy. The energy measurement from the the fluorescence detectors is used to cross calibrate the surface detectors, and makes the measurements made by the Auger Observatory surface detector highly model-independent. The calibration of the fluorescence detectors is then of the utmost importance to the measurements of the Ob- servatory. Described here are the methods of the absolute and multi-wavelength calibration of the fluorescence detectors, and improvements in each leading to a reduction in calibration uncertainties to 4% and 3.5%, respectively. Also presented here are the effects of introducing a new, and more detailed, multi-wavelength calibration on the fluorescence detector energy estimation and the depth of the air shower maximum measurement, leading to a change of 1±0.03% in the absolute energy scale at 1018 eV, and a negligible change in the measurement on shower maximum. ii Acknowledgements I am deeply grateful for the people this department has afforded me to meet. Wendy helped me to navigate the perilous logistics of graduate school, and still somehow remained my friend, and for that, I am eternally thankful. I am in the debt of the other graduate stu- dents that, like me, thought it was a good idea to go to graduate school. The friendships that formed in our shared misery, and the encouragement we offered one another are something I will cherish; including Leif for creating this LATEX dissertation document class. I could not imagine a better research group to be a part of. Alexei's attention to detail helped to further my understanding from cosmic ray particle physics to infrared soldering techniques. Jeff was the first member of the group I met when I visited seven years ago, and I will never forget his giddiness at the prospect of me attending CSU. If I only know how much time I would be spending in his office bouncing ideas of each other regarding calibration conun- drums, and various car maintenance issues, it was where most of my graduate education took place. John was suspiciously absent when I visited, but if he had been around I would not have believed he was going to be my advisor. His patience, (constant) reassurance, and willingness to chat physics or anything else are exceedingly rare qualities in a mentor that have helped me immeasurably. I am thankful for the support of my family, my mom and dad, and brother, who cultivated my scientific curiosities. Most of all I would like to acknowledge Sara. Her love and encouragement are what have kept me going. She is a continuous source of inspiration, whose confidence and support are what I admire and love greatly about her. Her willingness to listen to my prattling about my work and physics is a testament to her patience and virtue. And lastly, I cannot forget Ferdy, my writing buddy, he made sure everything made sense. iii Table of Contents Abstract . ii Acknowledgements . iii Chapter 1. Cosmic Rays . 1 1.1. Cosmic Origin of Contamination . 3 1.1.1. Victor Hess and his Discovery . 4 1.2. Detection Methods and Early Discoveries . 4 1.2.1. Detector Improvements . 5 1.2.2. The Beginnings of the Particle Zoo . 6 1.2.3. Air Showers and Very High Energies. 9 1.3. Current Understanding of Cosmic Rays . 11 1.3.1. The Extensive Air Shower (EAS) . 11 1.3.2. Glimpses of Composition . 15 1.3.3. Ground Arrays . 16 1.3.4. Particle Flux and the Cosmic Ray Energy Spectrum . 18 1.3.5. Energy Spectrum and Acceleration Mechanism Hypotheses . 20 1.3.6. The Cosmic Microwave Background and its Implications . 22 Chapter 2. The Pierre Auger Observatory. 26 2.1. The Surface Detector . 27 2.2. The Fluorescence Detector . 31 2.2.1. Fluorescence Light Detection . 32 2.2.2. The Pierre Auger Observatory Fluorescence Telescope . 33 2.2.3. The FD Camera. 36 iv 2.2.4. The PMT and Triggering Schemes . 37 2.2.5. Monitoring and Calibration. 39 2.3. Recent Extensions of the Observatory . 44 2.3.1. HEAT and AMIGA . 45 2.4. Overview of Results. 47 2.4.1. Energy Spectrum . 47 2.4.2. Composition . 49 Chapter 3. Calibration. 53 3.1. Surface Detector Calibration . 53 3.1.1. The vertical-equivalent Muon . 54 3.2. Fluorescence Detector Calibration. 57 3.2.1. Atmospheric Calibration. 58 3.2.2. Relative Calibration . 60 3.3. Absolute Calibration and the \Drum" Light Source . 63 3.3.1. The Drum and its Calibration . 63 3.3.2. Absolute Calibration of the Fluorescence Detectors . 77 3.3.3. Reduction of Uncertainties . 79 3.4. The Multi-wavelength Calibration. 80 3.4.1. History of the Multi-Wavelength Calibration. 81 3.4.2. Monochromator-based Multi-Wavelength Calibration . 84 3.4.3. The Multi-wavelength Drum Emission Spectrum. 90 3.4.4. Lab PMT Quantum Efficiency . 93 3.4.5. Uncertainties in Lab Measurements in Malarg¨ue. 96 3.4.6. Multi-Wavelength Calibration of the Fluorescence Detectors . 98 v 3.4.7. Uncertainties in FD Measurements . 99 3.4.8. Photodiode Monitor Data . 105 3.5. Calculation of the FD Efficiency . 105 3.5.1. FD Efficiency. 106 3.5.2. Final Uncertainty Calculation . 107 3.5.3. Comparisons Between Differently Constructed Telescopes . 108 3.5.4. FD Efficiencies . 110 3.6. New Calibrations: Now What? . 111 Chapter 4. The Effects of Calibrations on Measurements . 112 4.1. Hybrid Data . 113 4.1.1. Hybrid Geometry. 114 4.1.2. Measuring the Longitudinal Profile . 117 4.1.3. Fluorescence Yield . 118 4.1.4. Attenuation of Fluorescence Light . 120 4.2. Building the Analysis . 122 4.2.1. Shower Simulations. ..
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