Study of the Highest Energy Cosmic Rays

University Of Montana, Missoula MT

Investigators

Abstract

This proposal is a request for the continued NSF support of a particle astrophysics research program at the University of Montana. The focus of this proposal is on undergraduate research and outreach in conjunction with the High-Resolution Fly's Eye (HiRes), an air-fluorescence cosmic ray observatory and the leading active experiment in particle astrophysics today. In addition, a related new project, FLASH, will perform direct measurements of air fluorescence to better constrain HiRes systematic uncertainties. Cosmic rays have been known for a decade to strike the earth with energies exceeding 1020 electron-volts. The origins of these ultra-high-energy (UHE) particles, however, remain unclear. No single acceleration mechanism can explain all the features in the energy spectrum; the events appear to arrive with energies in excess of the Greisen-Zatsepin-Kuz'min (GZK) cutoff imposed by interactions with the cosmic microwave background; and no evidence for anisotropic behavior has yet been found in studies of UHE cosmic ray arrival directions. The HiRes experiment in western Utah is an ongoing and expanding project, which uses the nitrogen fluorescence technique to study UHE cosmic rays. HiRes aims to determine the energy spectrum, chemical composition, and arrival directions of these extraterrestrial particles, and thus provide data crucial to the development of modern astrophysical models. The FLASH (FLuorescence in Air from Showers) experiment at SLAC supports the aims of HiRes by seeking to perform a precise measurement of the fluorescence yield of charged particles in air. By reducing a potential source of systematic uncertainty in the HiRes measurement, FLASH will shed light on the apparent differences between spectra reported by HiRes and the previous-generation experiment, AGASA. FLASH will also provide data on airshower-induced fluorescence for future UHE cosmic ray experiments. In the education/outreach area, the University of Montana is an undergraduate institution in physics. Therefore this proposal is centered on undergraduate activity in experimental cosmic ray and elementary particle physics. The broader impact is significant; unique educational, research, and outreach opportunities in an underdeveloped region of the country.