Search for correlations of the arrival directions of high-energy cosmic neutrinos and highest-energy charged cosmic rays

带电宇宙射线的起源仍然是一个谜，即使在它们被发现100多年后。主要原因是它们在星系和星系外磁场中的偏转。只有在最高能量下，预期的偏转才足够小，可以尝试定向天文学。然而，即使世界上最大的天文台皮埃尔·奥格和望远镜阵列十多年来积累的统计数据，到目前为止也没有找到任何来源。一种很有希望的方法是将高能宇宙射线的方向与高能中性粒子、中微子和光子的观测联系起来。它们没有偏转，预计也会由加速宇宙射线的源或其附近产生。虽然几十TeV以上的高能光子已经在本地宇宙中被吸收了，但高能中微子是有希望的信使，因为它们可以在宇宙距离上几乎不受影响地传播。最近，冰立方中微子天文台发现了一种宇宙中微子流，其能量超过PeV。这种通量的来源尚未确定，但这种通量似乎主要是各向同性的，表明它是银河系外的起源。此外，通量归一化与从观测到的超高能量宇宙射线通量推导出的Waxman-Bahcall期望一致。为了评估这些通量之间的可能联系，并确定加速宇宙射线的天体物理来源，来自心宿二、冰立方、皮埃尔·奥格和望远镜阵列天文台的科学家们正在分析他们的数据，以确定方向相关性。结果，最初发现了微弱的迹象，但没有得到最新数据的证实。在本项目中，我们提出了后续分析，在中微子数据的统计、方向性信息和分析方法方面有了很大的改进。所有数据集的统计数据都增加了两倍以上，特别是具有良好指向的轨迹类事件的统计数据提高了大约四倍。使用这些轨迹事件的分析将基于一种新的、与磁偏转无关的可能性方法，通过明确拟合共同源的最可能位置。一个积极的观测结果将是一个科学突破，因为它将直接证明至少有一部分天体物理中微子流源相对接近我们的星系。中微子的精确定位将使我们能够直接确定宇宙射线的来源，并将这两个观测结果在多信使环境中联系起来。即使是与不相关假设相容的负结果，也可以用来约束宇宙射线和中微子的关系以及源和传播模型。

The origin of charged cosmic rays remains a mystery, even more than 100 years after their discovery. Main reason is their deflection in galactic and extra-galactic magnetic fields. Only at highest energies is the expected deflection sufficiently small to attempt directional astronomy. However, even with the accumulated statistics of more than a decade operation of the world-wide largest observatories Pierre Auger and Telescope Array, no sources could be identified to date. A promising approach is to correlate the directions of high-energy cosmic rays with observations of high-energy neutral particles, neutrinos and photons. These are not deflected and are expected to be produced also by or near the sources that accelerate cosmic rays. While high-energy photons above several tens of TeV are absorbed already within the local universe, high-energy neutrinos are promising messengers because they can propagate almost unaffected over cosmological distances. Recently the IceCube Neutrino Observatory has discovered a flux of cosmic neutrinos extending to above PeV energies. The sources of this flux have not been identified yet, but the flux appears largely isotropic indicating an extra-galactic origin. Furthermore, the flux normalization is consistent with the Waxman-Bahcall expectation that was derived from the observed flux of ultra-high-energy cosmic rays. In order to evaluate a possible connection between these fluxes and to identify the astrophysical sources that are accelerating cosmic rays, scientists from the Antares, IceCube, Pierre Auger and Telescope Array Observatories are analyzing their data for directional correlation. As a result, weak indications were found initially, which were, however, not confirmed by the most recent data. In this project we propose a follow-up analysis, which strongly improves in terms of statistics, directional information of the neutrino data and the analysis methods. The statistics of all data sets is increased by more than a factor two and particularly the statistics of track-like events with good pointing is improved by about a factor four. The analysis which is using these track-like events will be based on a new, magnetic-deflection-independent, likelihood method, by explicitly fitting for the most probable location of common sources. A positive observation would be a scientific breakthrough, as it would be direct evidence that at least a fraction of the sources of the astrophysical neutrino flux are relatively close to our galaxy. The good pointing of neutrinos would allow to directly pin-point the sources of cosmic rays and to connect these two observations in a multi-messenger context. Even a negative result compatible with a no-correlation hypothesis can be used to constrain the relation of cosmic rays and neutrinos as well as source and propagation models.