Boron nuclei in cosmic rays (CRs) are believed to be mainly produced by the fragmentation of heavier nuclei, such as carbon and oxygen, via collisions with the interstellar matter. Therefore, the boron-to-carbon flux ratio (B/C) and the boron-to-oxygen flux ratio (B/O) are very essential probes of the CR propagation. The energy dependence of the B/C ratio from previous balloon-borne and space-based experiments can be well described by a single power-law up to about 1 TeV/n within uncertainties. This work reports direct measurements of B/C and B/O in the energy range from 10 GeV/n to 5.6 TeV/n with 6 years of data collected by the Dark Matter Particle Explorer, with high statistics and well controlled systematic uncertainties. The energy dependence of both the B/C and B/O ratios can be well fitted by a broken power-law model rather than a single power-law model, suggesting the existence in both flux ratios of a spectral hardening at about 100 GeV/n. The significance of the break is about $5.6σ$ and $6.9σ$ for the GEANT4 simulation, and $4.4σ$ and $6.9σ$ for the alternative FLUKA simulation, for B/C and B/O, respectively. These results deviate from the predictions of conventional turbulence theories of the interstellar medium, which point toward a change of turbulence properties of the interstellar medium (ISM) at different scales or novel propagation effects of CRs, and should be properly incorporated in the indirect detection of dark matter via anti-matter particles.
Cosmic-ray Boron Flux Measured from 8.4 GeV$/n$ to 3.8 TeV$/n$ with the Calorimetric Electron Telescope on the International Space Station
我们提出的测量宇宙射线中的硼通量的能量依赖性和它的比例的碳通量\textcolor{black}{in an energy interval from 8.4 GeV$/n$ to 3.8 TeV$/n$}的基础上收集的数据的量热电子望远镜（CALET）在$\sim 6.4$年的操作在国际空间站。碳的能量谱的更新也提出了增加的统计比我们以前的测量。所观察到的硼通量显示出光谱硬化在相同的过渡能量$E_0 \sim 200$ GeV $/n$的C谱，虽然B和C通量有不同的能量依赖性。在$25 < E < 200$ GeV $/n$范围内，B谱的谱指数为$γ= -3.047\pm0.024$. B光谱通过$Δγ_B=0.25\pm0.12$硬化，而C光谱变化的最佳拟合值是$Δγ_C=0.19\pm0.03$。B/C通量比与$0.09\pm0.05$的硬化相容，尽管考虑到当前的统计不确定性，不能排除单一的幂律能量依赖性。B/C比能量依赖性的突破将支持AMS-02最近的观测结果，即次级宇宙射线比初级宇宙射线表现出更强的硬化。我们还进行了一个适合的B/C比与漏盒模型的宇宙射线在银河系中的传播，以探测一个可能的剩余值$λ_0$的平均逃逸路径长度$λ$在高能量。我们发现我们的B/C数据与$λ_0$的非零值兼容，这可以解释为宇宙射线在加速区域内穿过的物质的列密度。
Direct Measurement of the Cosmic-Ray Helium Spectrum from 40 GeV to 250 TeV with the Calorimetric Electron Telescope on the International Space Station
Observation of Spectral Structures in the Flux of Cosmic-Ray Protons from 50 GeV to 60 TeV with the Calorimetric Electron Telescope on the International Space Station
