从$X_{\rm max}$分布的尾部确定超高能量宇宙射线中的质子-氦比
Determination of the proton-to-helium ratio in cosmic rays at ultra-high energies from the tail of the $X_{\rm max}$ distribution
摘要：
本文提出了一种测量超高能宇宙射线中质子氦比的方法。它利用指数斜率，$Λ$，由空气淋浴实验测量的$X_{\rm max}$分布的尾部。该方法是相当强大的不确定性建模强子相互作用和系统误差的$X_{\rm max}$和能量，并可能存在的主要核比氦重。用空气簇射实验获得质子与氦的比率将是一项了不起的成就。为了量化的质量组成分析，尽管强子的不确定性，我们引入作为一个度量的“分析指标”的一个特定的质量敏感变量的适用性，并找到一个改进的性能相比，目前在文献中使用的其他变量的$Λ$方法。在$X_{\rm max}$分布的尾部中的事件的分数可以提供关于在初级束中比氦重的原子核的存在的附加信息。
英文摘要：
We present a method to determine the proton-to-helium ratio in cosmic rays at ultra-high energies. It makes use of the exponential slope, $Λ$, of the tail of the $X_{\rm max}$ distribution measured by an air shower experiment. The method is quite robust with respect to uncertainties from modeling hadronic interactions and to systematic errors on $X_{\rm max}$ and energy, and to the possible presence of primary nuclei heavier than helium. Obtaining the proton-to-helium ratio with air shower experiments would be a remarkable achievement. To quantify the applicability of a particular mass-sensitive variable for mass composition analysis despite hadronic uncertainties we introduce as a metric the `analysis indicator' and find an improved performance of the $Λ$ method compared to other variables currently used in the literature. The fraction of events in the tail of the $X_{\rm max}$ distribution can provide additional information on the presence of nuclei heavier than helium in the primary beam.
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