Detection of High Energy Neutrino and Gamma Ray

利用一个1000平方米的原型探测器，研究了在月球表面安装大型水切伦科夫探测器探测天体物理学起源的高能中微子的可行性。这些数据是在1992年初取得的。(1)触发率：高能中微子的信号是上行的μ子，它是由中微子与探测器下岩石的带电电流相互作用产生的。据估计，该通量是宇宙射线通量的10^数量级<-10>。这个巨大的背景已被抑制利用切伦科夫光的方向性。20”光电管已被放置在水面以下10米，5米的间隔。触发器要求4个以上光电管已命中，时间窗符合30 ns。即使使用这种简单的触发，也可以获得10^5量级的背景抑制，给出约4 Hz的触发速率。(2)事件的组成：事件的组成已被分析，使用的脉冲高度在检测器的上部，这是光学分离的检测器的主要部分。分析表明，大约一半的触发事件是由于空气簇射，它存款大脉冲高度的探测器的上部。其余的事件是由于具有大天顶角的μ子。(3)最后的背景抑制能力：20”光电管已通过1992-1993年购买的附加光电管使用宇宙射线μ子进行了校准。利用时间和脉冲高度信息的分析，产生约2 × 10 ~ 4的背景<10>抑制。我们认为，本研究的原始动机，即在表面上操作的大型水切伦科夫探测器的可行性，已经得到了证明。

Feasibility of a large water Cherenkov detector on the surface for high energy neutrinos of astrophysical origin was examined, using a 1000m^2 prototype detector. The data was taken in early part of 1992.(1) Trigger rate :The signal for high energy neutrino is upward-going muon, which is created by the charged current interaction of neutrino with rock under the detector. This flux is estimated to be an order of 10^<-10> of that of cosmic rays. This huge background has been suppressed by utilizing the directionality of the Cherenkov light.20" phototube has been placed 10m below the water surface, with 5m separation. The trigger requires more than 4 phototube has been hit with 30ns coincidence time window. Even with this simple trigger can attain a background suppression of the order of 10^5, giving about 4Hz trigger rate.(2) The composition of the events :The composition of the events has been analyzed, using the pulse height in the upper part of the detector which is optically separated from the main part of the detector. The analysis showed about half of the triggering events are due to air shower which deposit large pulse height in the upper part of the detector. The rest of the events are due to muons which have large zenith angle.(3) The final background rejection capability :The 20" phototube has been calibrated, using cosmic ray muons by the additional phototube which has been purchased in 1992-1993. An analysis, using both timing and pulse height information, yields about 2x10^<10> suppression of the backgrounds.We believe that the original motivation of this study, i.e.feasibility of operation of a large water Cherenkov detector on the surface, has been proved.