FLASH - FLuorescence in Air SHowers

这项提案要求资金对斯坦福直线加速器中心(SLAC)的电磁阵雨产生的空气荧光进行光谱分辨测量。该小组预计，这项实验将阐明两个超高能宇宙线(UHECR)实验HIRES和AGASA报告的结果之间的明显差异，并将为未来的UHECR实验提供可靠和迫切需要的簇射诱导荧光测试。该小组的目标是在总荧光产额和个别谱线上实现8%的准确度。实验还将验证我们对产额的能量依赖性的理解是正确的，精确到阵雨中有效的最低能量~100keV。SLAC的最终聚焦测试束(FFTB)电子线将以每个脉冲10^7到10^9的强度使用。他们建议同时使用薄靶和厚靶两种方法。薄靶运行将使他们能够测量每个光束轨迹的总荧光产额和光谱，达到8%。它还将允许精确测量产量和光谱对压力和大气杂质的依赖关系。束在厚靶中的相互作用模拟了宇宙线引起的空气簇射中电子能量的分布。一束有10^8个电子(~28GeV/电子)的束流的能量相当于2.8×10^18 eV的簇射能量。这些阵雨的叠加可以通过EGS和GEANT等软件来模拟。在厚靶实验中，将在簇射发展的不同深度测量荧光产额，以便与蒙特卡罗模拟进行详细比较。还将对混合了不同浓度的二氧化碳、Ar和水蒸气的空气或氮气进行测量。

This proposal requests funds to carry out a spectrally resolved measurement of air fluorescence produced by electromagnetic showers at Stanford Linear Accelerator Center (SLAC). The group expects that this experiment will shed light on the apparent differences between the results reported by two ultra high energy cosmic ray (UHECR) experiments, HiRes and AGASA, and will provide reliable and much needed tests of shower-induced fluorescence for future UHECR experiments.The group aims to achieve an accuracy of 8% in the total fluorescence yield and in the individual spectral lines. The experiment will also verify that our understanding of the energy dependence of the yield is correct down to the lowest energies effective in showers, ~100 keV. The Final Focus Test Beam (FFTB) electron line at SLAC will be used at intensities of 10^7 to 10^9 per pulse. They propose to use both thin target and thick target approaches. A thin target run will allow them to measure the total fluorescence yield per beam track, and the spectrum, to 8%. It will also allow a precise measurement of the dependences of the yield and spectrum on pressure and on atmospheric impurities. The interaction of the beam in a thick target mimics the distribution of electron energies found deep in cosmic ray induced air showers. A beam with 10^8 electrons (~28 GeV /electron) has an energy per bunch equal to that of a 2.8 x10^18 eV shower. The superposition of the showers can be modeled by software such as EGS and GEANT. In the thick target experiment the fluorescent yield will be measured at various depths in the shower development, allowing detailed comparison with the Monte Carlo simulations. Measurements on air or nitrogen mixed with various concentrations of CO2, Ar and water vapor will also be performed.