标题： 通过输运方程的视角探索超高能中微子实验 显示英文标题

标题： Exploring ultra-high energy neutrino experiments through the lens of the transport equation

摘要： 我们开发了一种基于视线近似中的输运方程的第一性原理形式，以将中微子望远镜处预期的μ子数量与地球表面的中微子通量联系起来。 我们计算了来自探测器附近中微子的上散射以及更远处产生的τ子衰变所产生的μ子在地球内部的分布。 该框架可以考虑系统不确定性，并澄清文献中常用定义背后的假设，例如有效面积。 我们将此形式应用于分析KM3NeT记录的高能μ子事件，其重建能量为$ 120^{+110}_{-60} \, \mathrm{PeV}$，仰角为$\left(0.54\pm 2.4\right)^\circ$，并与IceCube未观测到类似事件进行比较。 我们发现，在假设漫射中微子源具有幂律能量依赖性的前提下，两个实验之间存在$3.1\,\sigma$的矛盾。 结合两个数据集会导致KM3NeT处预期事件数非常低的偏好，这与观测数据形成鲜明对比。 在漫射源在KM3NeT能量处峰值以及稳定点源的情况下，矛盾都会增加，而瞬态源可能会将矛盾降低到$1.6\,\sigma$。 该形式可以处理潜在的超出标准模型的μ子来源，我们对此可能性进行了推测以解释这一矛盾。 显示英文摘要

摘要： We develop a first-principles formalism, based on the transport equation in the line-of-sight approximation, to link the expected number of muons at neutrino telescopes to the flux of neutrinos at the Earth surface. We compute the distribution of muons inside Earth, arising from the up-scattering of neutrinos close to the detector, as well as from the decay of taus produced farther away. This framework allows one to account for systematic uncertainties, as well as to clarify the assumptions behind definitions commonly used in literature, such as the effective area. We apply this formalism to analyze the high-energy muon event recorded by KM3NeT, with a reconstructed energy of $ 120^{+110}_{-60} \, \mathrm{PeV}$ and an elevation angle of $\left(0.54\pm 2.4\right)^\circ$, in comparison with the non-observation of similar events by IceCube. We find a $3.1\,\sigma$ tension between the two experiments, assuming a diffuse neutrino source with a power-law energy dependence. Combining both datasets leads to a preference for a very low number of expected events at KM3NeT, in stark contrast to the observed data. The tension increases both in the case of a diffuse source peaking at the KM3NeT energy and of a steady point source, whereas a transient source may reduce the tension down to $1.6\,\sigma$. The formalism allows to treat potential beyond-the-Standard-Model sources of muons, and we speculate on this possibility to explain the tension.