Detection of High Energy Neutrino and Gamma Ray

利用1000m^2的原型探测器，研究了在天体物理起源的高能中微子表面安装大型水切伦科夫探测器的可行性。这些数据是1992年初获得的。(1)触发率：高能中微子的信号是上行的Muon，它是由中微子与探测器下的岩石之间的带电相互作用产生的。这个流量估计是宇宙射线流量的10^-10&gt；数量级。这一巨大的背景被利用切伦科夫光的方向性进行了抑制。20英寸光电管被放置在水面以下10米处，间隔5米。触发要求4个以上的光管被击中，符合时间窗口为30 ns。即使有了这个简单的触发，也可以达到10^5量级的本底抑制，给出大约4赫兹的触发速率。(2)事件的组成：利用探测器上部的脉冲高度分析了事件的组成，该脉冲高度与探测器的主要部分光学分离。分析表明，大约一半的触发事件是由空气簇射引起的，空气簇射在探测器的上部沉积了很大的脉冲高度。(3)最后的背景抑制能力：利用1992-1993年购买的额外光管的宇宙线µ子，对20英寸光管进行了校准。利用时间和脉冲高度信息进行分析，得到了大约2x10；lt；10；gt；背景抑制。我们认为，这项研究的原始动机，即在地表运行大型水切伦科夫探测器的可行性已经得到证明。

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.