Abstract The observation of an ultra-high energy photon component of the cosmic radiation is one of the open problems in Astroparticle Physics. The stringent theoretical and experimental upper limits to the photon flux above 100 TeV make the search of a weak photon signal in the vast hadronic cosmic ray background a challenging task. At these energies, photon primaries entering the atmosphere develop an extensive air shower which is driven by electromagnetic processes with a poor muon component. The muon content of the air showers is one of the most promising observables that could lead to the best possible discrimination between photons and hadronic cosmic rays. In this article, we define a parameter capable of quantifying the muon component while reducing the fluctuations due to the unknown lateral distribution of muons. We explain the different features of this observable using simulated air showers between 30 and 300 PeV. We show that a merit factor of 5 in the separation between photon and proton primaries and a photon signal efficiency of at least ∼ 92% while rejecting 99.97% of the proton-initiated showers can be reached in the mentioned energy range of interest. This separation power can be achieved provided the shower features, specially the primary energy, are reconstructed sufficiently precise and without significant biases.

中文翻译：

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用于 30-300PeV 光子搜索的基于 μ 子的可观测物

摘要 宇宙辐射中超高能光子分量的观测是天体粒子物理学中的未解决问题之一。超过 100 TeV 的光子通量的严格理论和实验上限使得在广阔的强子宇宙射线背景中搜索微弱的光子信号成为一项具有挑战性的任务。在这些能量下，进入大气的光子初级会产生广泛的空气簇射，这是由具有弱介子分量的电磁过程驱动的。空气簇射中的 μ 子含量是最有希望的观测之一，它可能导致光子和强子宇宙射线之间的最佳区分。在本文中，我们定义了一个参数，该参数能够量化 μ 子分量，同时减少由于 μ 子的未知横向分布引起的波动。我们使用 30 到 300 PeV 之间的模拟空气淋浴来解释这个可观察对象的不同特征。我们表明，在提到的感兴趣的能量范围内，可以达到光子和质子原色之间分离的优值因子 5 和至少约 92% 的光子信号效率，同时拒绝 99.97% 的质子引发的簇射。如果淋浴特征，特别是初级能量，能够被足够精确地重建并且没有显着的偏差，则可以实现这种分离能力。