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

天体粒子物理学中的一个未解之谜是自然界如何将原子核加速到超过10^20 eV的能量。虽然较低能量的宇宙射线起源于我们的银河系内部，但最高能量的宇宙射线很可能来自更深的宇宙。对于能量在10^17 eV附近或以上的情况，预计会发生跃迁。为了找出跃迁发生的能量和方式，需要对宇宙射线的组成进行更精确的测量。目前，在这一能量范围内应用的技术是空气切伦科夫测量和地面空气簇射的粒子探测。第一个局限于天气好的黑夜，后者在解释大气中的粒子产生方面存在不确定性。另一种24/7工作的技术是无线电测量空气簇射。最近的发展表明，当与其他技术相结合时，它们在精度上具有竞争力，甚至可能更好。因此，本项目计划在西伯利亚贝加尔湖附近的通卡天文台同时进行联合收割机无线电、空气切伦科夫和粒子测量。多年来，莫斯科大学和伊尔库茨克国立大学都在该观测站进行空气簇射测量。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，又部署了一个额外的地面和地下粒子探测器阵列，用于粒子探测。在接下来的几年里，通过部署更多的伽马天文学专用探测器（TAIGA），该站点将成为俄罗斯领先的天体粒子物理中心之一。最后，该网站具有数字无线电阵列，Tunka-Rex（http：//www.ikp.kit.edu/tunka-rex/），我亲自负责。Tunka-Rex由44个天线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，但不可能重新申请。第一，现有的数据对分析很有价值。第二，从现在开始，使用新闪烁体阵列的持续混合测量将大大超过Tunka-133和其他实验目前可用的测量统计数据。因此，该提案要求在三年内提供总计433千欧元的资金，用于一名博士后，一名博士生和旅行。在开始时，分析将与现有的通卡-雷克斯事件进行，分析方法将进行优化，真正的混合分析，包括增重器。之后，可以分析大量的统计数据，以重建从银河系到河外宇宙射线过渡区中不同质量群的能谱。解释这些数据并将其与理论预测进行比较，最终将揭示河外宇宙射线究竟是以何种能量以及何种方式发挥作用。

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.