A 1000km3 Ultra-High Energy Neutrino Acoustic Detector

1000km3超高能中微子声探测器

• 批准号: 0457273
• 负责人: Giorgio Gratta
• 金额: --
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-04-01 至 2010-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0457273&HistoricalAwards=false
• 关键词: 1000km3; Ultra; Energy; Neutrino; Acoustic

In recent years scientists have expanded the horizon of astronomy by observing the Universe first with photons of increasingly smaller wavelengths and then by resorting to particles other than photons. The latest additions to our toolkit are neutrinos, neutral particles with a tiny mass, more than 500,000 times lighter than electrons. While the small mass of neutrinos make them already rather "exotic", it is now possible that ultra-high-energy neutrinos raining down to Earth from the outer space will help us understanding some catastrophic events in the universe. We do know that particles (possibly protons) of kinetic energies 1018 eV and above do occur in cosmic radiation and, in fact, some scientists claim to have observed cosmic rays with energies above 1020 eV. This is a tremendous energy for a single elementary particle, equivalent to the kinetic energy of a medium-sized book falling to the floor from a desk! As a comparison our most powerful particle accelerator can only accelerate protons to 1012 eV. We do not fully understand what kind of process can produce such high energy particles but, if also neutrinos of such high energies were to be produced we would have an important clue. The signals from such energetic particles would be dramatic enough to be recorded in conventional particle detector however the rate at which such energetic neutrinos would rain on Earth is expected to be so low that thousands of cubic kilometers of active material would be needed to have the chance of detecting some. A suitable detector cannot be built with nuts and bolts but it has to take advantage of an existing body of material! Ocean water is very common on the Earth surface and our group, with NSF support, is installing a system that will demonstrate the possibility of detecting ultra-high-energy neutrinos in cosmic radiation by the acoustic noise they are expected to produce when they interact and stop in sea water. Indeed their tremendous kinetic energy is expected to be converted into heat that would make the sea-water expand, producing a peculiar sound. The sound will be detected, in our initial study, by an array of hydrophones (underwater microphones) located off the coast of Florida and used by the US Navy for naval exercises. We have an agreement with the Navy that will allow us to install a special data acquisition system that will allow us to find the tiny pulses characteristic of the neutrino interaction in the large sea background caused by human activities and different sort of marine creatures. This project was initiated almost exclusively with undergraduate students. The initial feasibility study was done by Stanford Undergraduate Shaffique Adam, now at Cornell. The first data taking at the Navy array and the relative data analysis was performed by Stanford undergraduate Justin Vandenbroucke who is now working on the NSF Amanda/Ice Cube detectors in Antarctica as a Berkeley graduate student. A Stanford graduate student, Naoko Kurahashi, is leading the installation of the present system, while another Stanford undergraduate, Jason Kerwin, is building parts of a calibration device that we hope to use in the study.

近年来，科学家们首先用波长越来越小的光子观察宇宙，然后诉诸光子以外的粒子，从而扩大了天文学的视野。 我们的工具包中最新添加的是中微子，这是一种质量很小的中性粒子，比电子轻 500,000 倍以上。 虽然小质量的中微子已经相当“奇特”，但现在从外太空如雨点般落到地球的超高能中微子有可能帮助我们了解宇宙中的一些灾难性事件。 我们确实知道，动能 1018 eV 及以上的粒子（可能是质子）确实存在于宇宙辐射中，事实上，一些科学家声称观察到能量高于 1020 eV 的宇宙射线。 对于单个基本粒子来说，这是巨大的能量，相当于一本中等大小的书从桌子上掉到地板上的动能！ 相比之下，我们最强大的粒子加速器只能将质子加速到 1012 eV。 我们并不完全了解什么样的过程可以产生如此高能的粒子，但是，如果也能产生如此高能的中微子，我们将得到一个重要的线索。 来自此类高能粒子的信号足以在传统粒子探测器中记录下来，但此类高能中微子在地球上降雨的速度预计非常低，以至于需要数千立方公里的活性物质才有机会探测到一些中微子。 合适的探测器不能用螺母和螺栓来建造，但它必须利用现有的材料！ 海水在地球表面非常常见，我们的团队在美国国家科学基金会的支持下，正在安装一个系统，该系统将展示通过宇宙辐射中的超高能中微子在海水中相互作用和停留时产生的声学噪声来检测它们的可能性。 事实上，它们巨大的动能预计会转化为热量，使海水膨胀，产生一种特殊的声音。 在我们的初步研究中，这种声音将被位于佛罗里达州海岸附近的一系列水听器（水下麦克风）检测到，这些水听器被美国海军用于海军演习。 我们与海军达成了一项协议，允许我们安装一个特殊的数据采集系统，使我们能够找到人类活动和不同种类海洋生物引起的大海洋背景中中微子相互作用的微小脉冲特征。 该项目几乎完全是由本科生发起的。 最初的可行性研究是由现就职于康奈尔大学的斯坦福大学本科生 Shaffique Adam 完成的。 海军阵列的首次数据采集和相关数据分析是由斯坦福大学本科生 Justin Vandenbroucke 进行的，他现在作为伯克利研究生在南极洲从事 NSF Amanda/Ice Cube 探测器的工作。 斯坦福大学研究生 Naoko Kurahashi 正在领导本系统的安装，而另一位斯坦福大学本科生 Jason Kerwin 正在构建我们希望在研究中使用的校准设备的部件。