Decoding the composition of cosmic-rays in the transition region from 10^17 -10^18 eV with Tunka-Rex

天体粒子物理学的一个未解之谜是大自然如何将原子核加速到10^20 eV以上的能量。虽然能量较低的宇宙射线来自银河系内部，但能量最高的宇宙射线很可能来自更深的宇宙。对于能量在10^17 eV左右或以上的情况，跃迁是可以预料的。为了找出能量和跃迁是如何发生的，需要对宇宙射线组成进行更精确的测量。目前，在这个能量范围内应用的技术是空气-切伦科夫测量和地面空气阵雨的粒子探测。前者仅限于有好天气的黑夜，后者在解释大气中粒子产生方面存在不确定性。另一种全天候运行的技术是无线电测量空气淋浴。最近的发展表明，它们在精度方面具有竞争力，如果与其他技术相结合，甚至可能更好。因此，目前的提议计划在西伯利亚贝加尔湖附近的通卡天文台将同步无线电、空气切伦科夫和粒子测量结合起来。多年来，莫斯科和伊尔库茨克国立大学在这里进行气淋测量。自2009年以来，他们运行了一个由133个光电倍增管探测器组成的阵列，面积为1平方公里，名为Tunka-133。最近，一组额外的地面和地下闪烁体被部署用于粒子探测。在接下来的几年里，通过部署额外的伽玛天文学探测器（TAIGA），该地点将成为俄罗斯领先的天体粒子物理中心之一。最后，这个网站有一个数字无线电阵列，Tunka-Rex (http://www.ikp.kit.edu/tunka-rex/)，我个人负责。Tunka-Rex同时由44个天线组成，连接到空气切伦科夫和闪烁体阵列，并于2012年开始采集数据。部署和初步分析由亥姆霍兹俄罗斯联合研究小组资助，持续到2015年夏天，尽管取得了成功，但不可能再次应用。首先，已有的数据对分析是有价值的。其次，从现在开始，使用新的闪烁体阵列进行的混合测量将大大超过Tunka-133和其他实验目前可用的测量数据。因此，该提案要求为一名博士后和一名博士生提供为期三年的共计433欧元的资金，以及旅行。在开始时，分析将使用已经可用的Tunka-Rex事件进行，分析方法将优化为包括闪烁体的真正混合分析。随后，可以通过分析大统计量来重建星系外宇宙射线过渡区内不同质量群的能谱。解释数据并将其与理论预测进行比较，最终将揭示星系外宇宙射线究竟以何种能量以及以何种方式发挥作用。

One of the open mysteries in astroparticle physics is how nature accelerates atomic nuclei to energies of more than 10^20 eV. While cosmic rays at lower energies originate from inside our Milky Way, the highest energies most probably stem from the deeper universe. For energies around and above 10^17 eV the transition is expected. To find out at which energy and how the transition occurs, more accurate measurements of the cosmic-ray composition are needed.Currently, the techniques applied in this energy range are air-Cherenkov measurements and particle detection of air showers on ground. The first one limited to dark nights with good weather, the latter one suffers from uncertainties in interpreting the particle production in the atmosphere. An alternative technique operating 24/7 are radio measurements of air showers. Recent developments indicate that they can be competitive in precision, and maybe even better, when combined with the other techniques. Thus, the present proposal plans to combine simultaneous radio, air-Cherenkov, and particle measurements at the Tunka observatory close to Lake Baikal in Siberia.Since many years Moscow and Irkutsk State Universities perform air-shower measurements at this site. Since 2009 they operate an array of 133 photomultiplier detectors with 1 km² area named Tunka-133. Recently, an additional array of over- and underground scintillators was deployed for particle detection. In the next years, the site will emerge to one of the leading astroparticle physics centers in Russia by deploying additional detectors dedicated to gamma astronomy (TAIGA). Finally, the site features a digital radio array, Tunka-Rex (http://www.ikp.kit.edu/tunka-rex/), for which I am personally responsible.Tunka-Rex consists of meanwhile 44 antennas connected to the air-Cherenkov and scintillator arrays, and started data taking in 2012. The deployment and initial analyses were funded by a Helmholtz Russian Joint Research Group running until summer 2015, without possibility for reapplication - despite of its success. First, the already available data are valuable for analysis. Second, from now on continued hybrid measurements with the new scintillator array will exceed significantly the statistics of presently available measurements by Tunka-133 and other experiments.For this reason, the proposal requests funding of in total 433 kEUR for a period of three years, for one postdoc, one PhD student, and travels. At the beginning, the analysis will be performed with the already available Tunka-Rex events, and analysis methods will be optimized for a true hybrid analysis including the scintillators. Later, large statistics can be analyzed to reconstruct energy spectra for different mass groups in the transition region from galactic to extra-galactic cosmic rays. Interpreting the data and comparing them to theoretical predictions finally will reveal at which energy exactly and in which way extragalactic cosmic rays come into play.