Study of the Highest Energy Cosmic Rays

本提案是对美国国家科学基金会继续支持蒙大拿大学粒子天体物理学研究项目的请求。该提案的重点是本科生的研究和推广，与高分辨率苍蝇之眼（HiRes）相结合，这是一个空气荧光宇宙射线天文台，也是当今粒子天体物理学中领先的活跃实验。此外，一个相关的新项目FLASH将对空气荧光进行直接测量，以更好地约束HiRes系统的不确定度。十年前，人们就知道宇宙射线以超过1020电子伏特的能量撞击地球。然而，这些超高能量（UHE）粒子的起源仍不清楚。没有一种单一的加速机制可以解释能量谱中的所有特征；这些事件的能量似乎超过了与宇宙微波背景相互作用所施加的Greisen-Zatsepin-Kuz'min （GZK）截止值；在对超高能宇宙射线到达方向的研究中，还没有发现各向异性行为的证据。犹他州西部的HiRes实验是一个正在进行和扩大的项目，它使用氮荧光技术来研究UHE宇宙射线。HiRes的目标是确定这些外星粒子的能谱、化学成分和到达方向，从而为现代天体物理模型的发展提供至关重要的数据。SLAC的FLASH（来自阵雨的空气中的荧光）实验通过寻求对空气中带电粒子的荧光产率进行精确测量来支持HiRes的目标。通过减少HiRes测量中系统不确定性的潜在来源，FLASH将揭示HiRes报告的光谱与上一代实验AGASA之间的明显差异。FLASH还将为未来的UHE宇宙射线实验提供有关雨淋诱导荧光的数据。在教育/推广领域，蒙大拿大学是一所物理学本科院校。因此，本建议以本科生在实验宇宙射线和基本粒子物理方面的活动为中心。更广泛的影响是显著的；在该国欠发达地区提供独特的教育、研究和推广机会。

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.