中微子物理

INTRODUCTION TO NEUTRINO PHYSICS

近十几年来积累的数据表明 ,有相当数量的太阳中微子流在从太阳到地球探测器的漫长旅程中丢失了 .最新的大气中微子实验结果指出 ,宇宙射线引起的大气中νμ 与νe 的比例不是原有理论预言的 2∶1,而是接近 1∶1,而且发现从上而下的νμ 数目比从下而上的多 ,νe 的数量却基本不变 .这两种现象可能是源于中微子振荡或其他的机制 ,然而这些机制并没有包含在 2 0世纪最成功的理论———最小标准模型中 .换言之 ,要合理解释所观测到的中微子实验就一定存在超越标准模型的新物理 .人们期望在 2 1世纪通过对中微子物理的进一步研究 ,对物质世界的结构、宇宙的演化以及基本相互作用获得更新的理解 .

The data accumulated in the past decades indicate that a certain fraction of neutrino flux radiated from the Sun is lost on the way to the Earth detectors. Recent experiment on atmospheric neutrino show that the ratio of ν μ and ν e particles produced due to cosmic rays is not 2∶1, as predicted by the present theory, but almost 1∶1. Moreover, the upward flux of ν μ is less than the downward flux but for ν e both are almost equal. These two phenomena may be caused by the neutrino oscillation or other mechanisms which are not included in the minimal Standard Model, the most successful theory of the 20th century. In other words, to reasonably interpret the observed experimental results on neutrinos, one definitely needs some new physics beyond the Standard Model. We can hope that in the 21st century, through further study on neutrino physics, we can gain better understanding about the matter structure, universe evolution and fundamental interactions.