Speaker
Description
The origin of the knee structure in cosmic ray (CR) energy spectrum remains unresolved. Various types of models have been proposed to explain it, which can be distinguished as acceleration origin (due to the limitation of the maximum possible CR energy by Galactic sources), propagation origin (because of the transition from slow to fast diffusion of Galactic CRs), interaction origin and local source origin. This work focuses on the propagation origin by adopting a double power law rigidity-dependent diffusion coefficient $D(\mathcal{R}) \propto\left\{\begin{array}{c}\mathcal{R}^\delta, \mathcal{R} \leq \mathcal{R}_{\text {knee }} \\ \mathcal{R}^{\delta+\delta_{\text {knee }}, \mathcal{R}>\mathcal{R}_{\text {knee }}}\end{array}\right.$, where $\mathcal{R}_{\text {knee }}$ is the break rigidity and $\delta_{\text {knee }}$ is the index change. By comparing DRAGON calculation with spectra measured by KASCADE, we found $\mathcal{R}_{\text {knee }}\approx1.0\rm{PV}$ and $\delta_{\text {knee }}\approx1.0$. However, giving the above rigidity parameter, the large scale anisotropy observation above 100TeV strongly disfavors this $\delta_{\text {knee }}$ value. Large scale anisotropy suggests that index change is smaller than 0.15 at 95% CL. The propagation origin of the knee is therefore excluded by the anisotropy measurement with a high confidence level.
