HELIX - the High Energy Light Isotope eXperiment

HIRIX(高能光同位素实验)被设计用来测量持续轰击地球的带电宇宙射线。宇宙射线是在一个多世纪前被发现的，尽管多年来人们已经对它有了很多了解，但许多谜团仍然存在。例如，众所周知，它们主要由氢和氦的原子核组成，但也有少量较重的原子核。宇宙射线被地球大气层阻挡，因此有关宇宙射线的大部分信息来自部署在太空或高度超过35公里的气球上的粒子探测器。 由于宇宙射线是带电的，它们的轨迹会受到银河系中磁场的影响而弯曲，而且它们不会回到起源地，所以宇宙射线的来源并没有被明确地识别出来。尽管存在不确定性，但人们可以使用宇宙线产生和传播的模型来了解当地的银河系邻居。Helix的目的是提供关键的测量结果，帮助我们在银河系环境的相互竞争的模型中做出决定，并帮助我们了解附近星际空间的性质。 这种测量的动机是最近发现的，宇宙射线流量中正电子与电子的比例随着能量的增加而上升。这种效应已经通过几个独立的实验进行了测量，并被认为要么是由于附近来源的粒子产生，要么是由于暗物质粒子的湮灭或衰变。暗物质的解释是诱人的，因为这些难以捉摸的粒子已经在加速器、低背景的地下实验室和伽马射线天文望远镜上进行了30多年的密集搜索。要在这两种解释之间做出选择，人们需要更好地了解我们银河系附近的部分。 Helix将通过测量铍核的两个同位素Be9和Be10的相对流量来探测当地环境。两者都是由较重的原子核与星际介质碰撞产生的，但Be10具有放射性，衰变的半衰期为140万年；它是一种“时钟同位素”。在一个类似于碳测年的过程中，人们可以使用两个同位素的流量比来计算它们已经旅行了多长时间，经过了什么。为了进行测量，Helix将使用一台磁光谱仪，其中包括超导磁体和一套在典型粒子物理实验中发现的组件。有效载荷将由2019年从南极洲海岸发射的大型氦气球携带到太空边缘。它将在高空停留两周，24小时全天候环绕欧洲大陆飞行。超导磁体提供的高分辨率和长途飞行产生的卓越统计功率的结合，将使测量能够在以前从未探索过的能量范围内进行，而这是一个理论最需要指导的领域。

The HELIX (High-Energy Light Isotope eXperiment) is designed to measure the charged cosmic rays that continually bombard the Earth. Cosmic rays were discovered just over a century ago and, although much has been learned about them over the years, many mysteries remain. It is known, for example, that they mostly comprise the nuclei of hydrogen and helium, but there are lesser amounts of heavier nuclei as well. Cosmic rays are blocked by the Earth's atmosphere so most information about them comes from particle detectors deployed in space or on balloons at altitudes in excess of 35 km. Since cosmic rays are electrically charged, their trajectories are curved by magnetic fields in the galaxy and they do not 'point back' to their place of origin so the sources of cosmic rays have not been unambiguously identified. Despite the uncertainties, one can use models of cosmic-ray production and propagation to learn about the local galactic neighbourhood. The purpose of HELIX is to provide key measurements that will help decide among competing models of our galactic environment and help us understand the nature of nearby interstellar space. The motivation for such measurements is the recent discovery of a rise with energy of the ratio of positrons to electrons in the cosmic-ray flux. This effect has been measured by several independent experiments and is thought to be due either to particle production in nearby sources or to the annihilation or decay of dark-matter particles. The dark-matter explanation is tantalizing since these elusive particles have been the subject of intense searches for more than three decades at accelerators, in low-backgound underground laboratories, and with gamma-ray astronomy telescopes. To decide between these two explanations one needs a better understanding of the nearby part of our galaxy. HELIX will probe the local environment by measuring the relative flux of two isotopes of the beryllium nucleus, Be9 and Be10. Both are produced by collisions of heavier nuclei with the interstellar medium but Be10 is radioactive and decays with a half-life of 1.4 million years; it is a 'clock isotope'. In a procedure analogous to carbon dating, one can use the flux ratio of the two isotopes to calculate how long, and through what, they have been travelling. To make the measurement, HELIX will use a magnetic spectrometer comprising a superconducting magnet and a suite of components found in a typical particle-physics experiment. The payload will be carried to the edge of space by a large helium balloon launched from the coast of Antarctica in 2019. It will remain aloft for two weeks, circumnavigating the continent in 24-hour daylight. The combination of high-resolution afforded by the superconducting magnet and superior statistical power resulting from the long flight will enable measurements to be made in a previously unexplored energy range, a region where theory needs the most guidance.