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作用产生的GZK效应产生的。宇宙线由于大爆炸或一种活跃的星系核等产生的中微子的作用而损失能量。中微子是可能旅行到很长宇宙距离的最高能量粒子。因此，只有超中微子才能给我们提供大爆炸前后高能态的直接信息。超高能中微子的通量很低，所以我们需要非常大的探测介质来进行探测。我们关注的是天然岩盐矿，它对无线电波具有巨大的质量和较长的衰减长度。超高能中微子与岩盐相互作用时产生的电磁簇射可以通过阿斯基恩效应产生无线电波。天鹅座效应实质上是电磁簇射中过剩电子之间的相干切伦科夫效应。我们用微扰腔谐振法测量了1 GHz和0.3 GHz的衰减长度。1)合成样品和霍克利样品的最大衰减长度(200m-500m)将在0.5 GHz到2 GHz之间。2)经济的天线阵间距在350米左右就可以探测到GZK中微子。3)在盐岩中，衰减长度具有频率依赖性。4)霍克利样品的衰减长度随频率从0.3 GHz增加到1 GHz。水在岩盐晶体或卤水中封闭在岩盐内部可能会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.