HELIX - the High Energy Light Isotope eXperiment

HELIX（高能光同位素实验）被设计用来测量不断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，尽管多年来人们对它有了很多了解，但仍有许多谜团未解。例如，众所周知，它们主要由氢和氦的原子核组成，但也有少量的较重的原子核。宇宙射线被地球的大气层所阻挡，所以关于宇宙射线的大部分信息来自于部署在太空中的粒子探测器或在超过35公里高度的气球上。******由于宇宙射线是带电的，它们的轨迹被星系中的磁场弯曲，它们不“指向”它们的原点，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，人们还是可以利用宇宙射线产生和传播的模型来了解当地的星系邻居。HELIX的目的是提供关键的测量数据，帮助我们在银河系环境的竞争模型中做出决定，并帮助我们了解附近星际空间的性质。******进行这种测量的动机是最近发现宇宙射线通量中正电子与电子的能量之比随着能量的增加而增加。这种效应已经被几个独立的实验测量到，并且被认为是由于附近源的粒子产生或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、低背景地下实验室和伽玛射线天文望远镜上进行了30多年的密集研究。要在这两种解释之间做出选择，我们需要对银河系附近的部分有更好的了解。******HELIX将通过测量铍核的两种同位素Be9和Be10的相对通量来探测当地环境。两者都是由较重的原子核与星际介质碰撞产生的，但Be10是放射性的，半衰期为140万年；它是一种“时钟同位素”。在类似于碳定年法的程序中，人们可以使用两种同位素的通量比来计算它们经过了多长时间和什么过程。为了进行测量，HELIX将使用由超导磁体和典型粒子物理实验中发现的一套组件组成的磁谱仪。该有效载荷将于2019年由一个从南极洲海岸发射的大型氦气球携带到太空边缘。它将在空中停留两周，在24小时的日光下环绕欧洲大陆。超导磁体提供的高分辨率和长途飞行带来的优越统计能力的结合，将使测量能够在以前未开发的能量范围内进行，这是理论最需要指导的区域。*****

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.*****