區域地層結構對極高能天文微中子觀測影響

Abstract

本文針對極高能天文微中子與地球交互作用進行研究，藉由引入位於南極且具有冰層厚度與海床高程的BedMap2數位高程模型(DEM)，增添當地高能天文微中子與地表層真實環境的蒙地卡羅法模擬。模擬前先由DEM計算出一些目前位於南極，建置中或已建置完成之微中子觀測實驗位置上，各方向的傾斜深度。以傾斜深度計算結果選定位於羅斯冰棚的ARIANNA實驗位址，並套用較為符合其實驗設計概念的圓餅狀偵測器敏感區(DSR)，進行單能量的高能天文濤子微中子模擬。得出模擬結果後初步探討引入模型時，DSR中各方向與各類事件的事例數角分布，以及引起簇射的事例數能量分布。事例數角分布方面，模擬結果符合根據傾斜深度所推論的結果，對於一些特定種類與天頂角方向的事件，有事例數的方位角分布差異：對於能量10^10 GeV與10^10.5 GeV微中子，淺穿地球微中子在本研究定義之方位角210至300度之間，首次發生的電性流(CC)與中性流(NC)交互作用事件有相對較低的事例數；而以濤子衰變占多數的下行微中子所引發再生事件，在方位角210至240度之間則有相對較高的事例數。而再生事件中，濤子衰變與其他交互作用引起的簇射能量分布也有顯著的差異。

This is a research of the interaction between ultra-high energy astrophysical neutrinos and earth. By introducing the BedMap2 digital elevation model, which has the ice thickness, bed elevation, and surface elevation that are located in Antarctica, we performed Monte-Carlo simulation on the interaction between neutrinos and the local terrain. Before performing the simulation, we selected some locations of astrophysical neutrino observation experiments. Then we calculated the slant depth of all directions by an algorithm and a numerical integration method. Referring to these results, we selected the location of ARIANNA which is located at Ross shelf for our simulations. We constructed a disk shape detector sensitive region for our simulations and generated monoenergetic tau neutrinos at some energy levels between 10^8 GeV and 10^10.5 GeV. The simulation results coincide with our predictions which are according to the slant depth calculations. For 10^10 GeV and 10^10.5 GeV neutrinos we generated, the number of first-generated earth-skimming (The zenith angle θ is between 90° and 91°.) events is relatively low when the azimuth angle φ is between 210° and 300° (Reference vector is pointed to south.). However, the number of regenerated down-going (0° ≤ θ ≤ 89.5°) events is relatively high when 210° ≤ φ ≤ 240°. Most of the regenerated events are tau decay events. For regenerated events, the distributions of shower energy have significant differences between the showers which are created by tau decay and other interaction events.