Basic research on salt neutrino detector for ultra high energy neutrino

超高能中微子是由超高能宇宙线与宇宙微波背景辐射相互作用产生的GZK效应。UHE宇宙射线通过UHE中微子的作用失去能量，中微子应该是在大爆炸或一种活动星系核等产生的。中微子是可能在很长的宇宙距离内旅行的最高能量粒子。因此，只有UHE中微子能直接给出大爆炸前后高能态的信息。UHE中微子的通量非常低，因此我们需要非常大量的探测介质来进行探测。天然岩盐矿是一个质量巨大、电波衰减长度长的矿山，受到人们的广泛关注。UHE中微子与岩盐相互作用产生的电磁簇射可以通过Askaryan效应产生无线电波。Askaryan效应实质上是电磁簇射中多余电子之间的相干切伦科夫效应。用微扰谐振腔法测量了1GHz和0.3GHz的衰减长度。测量结果总结如下：1）最大衰减长度（200 m-500 m）在合成样品和Hockley样品（Texas）上的衰减长度将在0.5 GHz-2 GHz之间。2）间距在350 m左右的经济型天线阵列可以探测到GZK中微子。3）岩盐中的衰减长度具有频率依赖性。4）从0.3GHz到1GHz，Hockley的衰减长度随频率的增加而增加。岩盐晶体中的水或封闭在岩盐内部的盐水可缩短频率范围内的衰减长度。

Ultra high energy (UHE) neutrino should be generated by GZK effect by a reaction between UHE cosmic ray and cosmic microwave background. UHE cosmic ray loses the energy by the effect UHE neutrino should be generated at the big bang or a sort of active galactic nuclei etc. Neutrino is the highest energy particle possible to travel very long cosmic distance. Therefore only UHE neutrino gives us directly information of high energy state at the big bang or so. The flux of UHE neutrino is very low, so we need very massive detection media to detect. We pay attention to natural rock salt mine which has a huge mass and long attenuation length for radio wave. Radio wave could be generated through Askaryan effect by electromagnetic shower occurred at the interaction between UHE neutrino and rock salt. Askaryan effect is essentially a coherent Cherenkov effect between excess electrons in the electromagnetic shower. We measured the attenuation length at 1GHz and 0.3GHz by a perturbation cavity resonator method. The summary of the measurement is as follows.1)The largest attenuation length (200m-500m) will be between 0.5GHz and 2GHz at the synthetic and Hockley sample (Texas).2)Economical antenna array with the spacing around 350m could detect GZK neutrino.3)The attenuation length has frequency dependence in rock salts.4)The attenuation length of Hockley increases with respect the frequency from 0.3GHz to 1GHz. Water in rock salt crystal or brine closed inside at the rock salt may shortens the attenuation length in the frequency range.