The Telescope Array and its Low Energy Extention

望远镜阵列（TA）项目是日本-美国-中国-台湾在超高能宇宙射线物理学领域的努力。 该实验旨在探测和测量宇宙中最强大的粒子，这些粒子可以在单个原子核中携带与快速投球棒球一样多的能量。 这种粒子非常罕见。 TA借鉴了之前两个较小实验的技术专长，即1993年至2003年在日本进行的Akeno Giant Air Shower Array实验（AGASA）和1997年至2006年在犹他州进行的高分辨率蝇眼实验（HiRes）。 当UHECR进入地球的高层大气时，它与大气核相互作用，产生次级粒子喷雾，这些次级粒子随后与大气深处的更多核碰撞，等等。这种粒子雪崩被称为广泛空气簇射（EAS）。 AGASA使用111个（2平方米）探测器单元阵列测量了地面上EAS的足迹，每个探测器单元都计算了通过它的粒子数量。HiRes通过成像带电粒子穿过空气时发出的荧光来观察EAS的纵向发展。 TA将这两种技术结合在一个单一的位置，然后给出一个更完整的图片，每一个宇宙射线事件比单独的技术。 TA项目由日本文部科学省和美国国家科学基金会共同资助，由犹他州大学主办。 它位于犹他州三角洲镇附近。 该位置结合了地面阵列所需的400多平方英里未开发土地的优势以及Delta提供的基础设施支持。 沙漠环境对于荧光探测器的运行至关重要，荧光探测器在晴朗无月的夜晚运行，需要清洁干燥的空气才能获得最大的透明度。 TA在2007年春季完成后，将成为北方最灵敏的宇宙射线探测器。 TA的合作机构包括来自日本的15所大学和实验室，由东京大学宇宙射线研究所（ICRR）领导。 美国的合作者包括六所大学和洛斯阿拉莫斯国家实验室。 参加的还有来自中国北京高能物理研究所（IHEP）和台湾国立联合大学的科学家。 TA的目标之一将是找到UHECR的来源，怀疑是活动星系核（AGN）。活动星系核，占所有已知星系的10%。 它们是宇宙中已知的能量最大的天体之一。 AGN被认为是由中心黑洞中物质和能量的吸积提供动力的。 AGASA和HiRes的实验都观测到了宇宙射线源和活动星系核之间的相关性，这些星系的一个子类被称为BL-撕裂天体（BL-Lac），它们的喷流指向地球。 大多数已知的活动星系核和BL-Lac天体都是在北方的天空中发现的，远离我们银河系在南半球突出的遮蔽。 此外，TA将研究UHECR与宇宙微波背景辐射之间相互作用预计会发生GZK抑制的能量区域。 当碰撞中存在足够的能量产生一种称为π介子的短寿命粒子时，这种相互作用就会变得很大。 HiRes最近报道了这种抑制的强有力证据，但AGASA的结果显示没有这种减轻。 对这种差异的一个可能的解释是实验之间的能量尺度差异;这将通过同时观察两种类型的探测器来解决。另一种可能性，由于有限的统计数据造成的波动，将由TA用一个八倍于AGASA的地面阵列来解决。 HiRes项目在ASPIRE有一个长期的更广泛的影响项目，该项目涉及UHECR科学的许多层次的教师和学生。 此外，TA将在三角洲镇建立一个游客中心，欢迎游客参观其网站。

The Telescope Array (TA) Project is a joint Japan-U.S.-China-Taiwan effort in the field of ultra high energy cosmic ray (UHECR) physics. This experiment is designed to detect and measure the most powerful particles in the Universe, which can carry as much energy in a single atomic nucleus as a fast pitch baseball. Such particles are very rare. TA draws on the technical expertise of two previous smaller experiments, the Akeno Giant Air Shower Array experiment (AGASA), which operated between 1993-2003 in Japan and the High Resolution Fly's Eye (HiRes) experiment that ran between 1997 and 2006 in Utah. When an UHECR enters the upper atmosphere of the Earth, it interacts with an atmospheric nucleus to produce a spray of secondary particles, which subsequently collide with more nuclei deeper in the atmosphere, and so on. This avalanche of particles is known as an Extensive Air Shower (EAS). AGASA measured the footprint of EASs at ground level using an array of 111 (2-m2) detector units each of which counted the number of particles passing through it. HiRes observed the longitudinal development of EASs by imaging the fluorescence light emitted by the charged particles as they passed through air. TA combines these two techniques in a single location, which then gives a more complete picture of each cosmic ray event than could either technique alone. The TA Project is being jointly funded by the Ministry of Education, Culture, Sports, Science and Technology in Japan, and the National Science Foundation in the United States, and is hosted by the University of Utah. It is located near the town of Delta, Utah. The location combines the advantages of more than 400 square miles of undeveloped land needed by the ground array with infrastructure support provided by Delta. The desert environment is essential for the operation of fluorescence detectors, which run on clear, moonless nights and require clear, dry air for maximum transparency. After its completion in the spring of 2007, TA will be the most sensitive cosmic ray detector in the Northern Hemisphere. The collaborating institutions on TA include 15 universities and laboratories from Japan, led by the Institute for Cosmic Ray Research (ICRR) at the University of Tokyo. The U.S. collaborators include six universities and Los Alamos National Laboratory. Also participating are scientists from the Institute for High Energy Physics (IHEP) in Beijing, China, and the National United University of Taiwan. One of the goals of TA will be to find the sources of UHECRs, suspected to be active galactic nuclei (AGN). AGN's, which comprise about 10% of all known galaxies. These are among the most energetic objects known in the Universe. AGNs are thought to be powered by accretion of matter and energy in a central black-hole. Correlations between cosmic ray sources and AGNs have been observed by both the AGASA and HiRes experiments, with a subclass of these galaxies, called BL-Lacerate (BL-Lac) objects, which have their jets pointed toward Earth. Most of the known AGN's and BL-Lac objects are found in the Northern sky, away from the obscuration of our own Milky Way Galaxy that is prominent in the Southern Hemisphere. In addition, TA will study the energy region where the Greisen-Zatsepin-K'uzmin (GZK) suppression of the UHECRs is expected to occur from interactions between UHECRs and the Cosmic Microwave Background Radiation. This interaction becomes large when sufficient energy exists in the collisions to produce a short-lived particle called the pi-meson. HiRes has recently reported strong evidence for this suppression, but AGASA's results show no such abatement. A possible explanation for this discrepancy is an energy scale difference between the experiments; this will be resolved by simultaneous observation with both type of detectors. Another possibility, fluctuations due to limited statistics, will be addressed by TA with a ground array eight times the size of AGASA. The HiRes project has had a longstanding broader impacts project in ASPIRE, which has involved teachers and students at many levels in the science of UHECRs. In addition, TA will build a visitors center in the town of Delta, which will welcome visitors to its site.