A Cherenkov Radiation Detector for the Auger Project Katarzyna Oldak

1. A Cherenkov Radiation Detector for the Auger Project Katarzyna Oldak Research Adviser: Corbin Covault Department of Physics High Voltage Power Supply Tube PMT Ammeter Number Abstract Detector Design Panel Spacing The purpose of this project was to put together a durable and low-cost Cherenkov radiation detector from a non-imaging optical concentrator and a coincidence system. The goal was to detect Cherenkov radiation from the atmosphere under clear and dark skies. The design of the detector consists of a central photomultiplier tube (PMT) with a Winston-cone optical concentrator used to increase light collection and to block out ambient light from above the horizon. Four scintillator panels and a coincidence unit are used to identify muon showers, which come down simultaneously with Cherenkov radiation. This project attempts to find an alternate method of detecting Cherenkov radiation and further the study of the origin and composition of ultra-high-energy cosmic rays. Energy Figure 6. A log-log plot of the predicted distribution of air showers detected by the apparatus. Figure 7. Scintillator panels with predicted shower sizes. Figure 3. A schematic of the apparatus. • A Winston-cone concentrator, designed to only collect light from within 40º of the zenith, increases the light collecting area of the PMT as well as keeps out light pollution from city lights. • The material in the scintillator panels reacts with muons and releases photons, which are in turn detected by a PMT mounted on each panel. The scintillators are housed in red crab boxes (see Figure 3) and their signals are put together in a coincidence unit. As an air shower hits the ground, the spread of the falling particles depends on the initial energy of the cosmic ray. More energetic cosmic rays create larger circles on the ground and are therefore easier to detect. However, more energetic cosmic rays enter the atmosphere less frequently than slower rays, so their observed number is smaller. The spacing of the scintillator panels determines the minimum energy that can be detected with the apparatus. A 15 m spacing between panels allows the apparatus to detect showers generated by cosmic rays with energies of 50-200 TeV. Figure 1. A projection of the celestial sphere. Active galactic nuclei are marked by asterisks. Arrival directions of 27 most energetic cosmic rays detected by the Pierre Auger Observatory are marked by circles. Sky Brightness Background • Is the Cleveland sky too bright to use this detector? • The goal is to detect single Cherenkov radiation photons against the background light from stars. Future Work Detecting Cherenkov radiation is a way of obtaining information about the cosmic rays that enter the Earth’s atmosphere. The radiation is a bluish glow emitted by particles traveling faster than the speed of light in a given medium. Ultra-high energy cosmic rays (UHECRs) have energies of eV and they interact to form extensive particle showers. The goal of this project is to come up with a third data collecting method for the Pierre Auger Collaboration, which is currently employing two different methods of studying UHECRs. The Collaboration is attempting to identify the sources and composition of these cosmic rays. If it is possible to construct a low-cost, durable apparatus that can detect Cherenkov radiation occuring in the atmosphere, the Pierre Auger Collaboration may be able to employ such detectors to collect more data about ultra-high-energy cosmic rays. In order to reach this goal, more component testing and design work may need to be done. Figure 4. A schematic of the apparatus used to measure sky brightness. Acknowledgements • Only a small solid angle of the sky was exposed to the PMT held at various angles. • Calculating the total brightness showed that the Cleveland sky would cause a 1.6 mA current. Since the PMT saturates at 1.3 mA, Cherenkov radiation would not be detected. I would like to thank my adviser Corbin Covault for all this help and guidance. I also extend special thanks to Ross Burton for his assistance with this project as well as Joe Liang for his work on the scintillator panels. I would also like to thank all other members of the High Energy Astrophysics group at CWRU as well as the Pierre Auger Collaboration. References • The Pierre Auger Collaboration et al. “Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Object.” Science. 318, 5852 (9 November 2007) (url: http://www.sciencemag.org/cgi/content/full/318/5852/938) • Pierre Auger Observatory. Retrieved April 5, 2009, Web site: http://www.auger.org • Cendes, Yvette. “The Test and Feasibility of a Cherenkov Detector for the Auger Project.” May 2008. Figure 2. An extensive air shower caused by an ultra-high-energy cosmic ray entering the atmosphere. Figure 5. Cleveland sky measurements.