Determination of the electron neutrino rest mass via tritium decay

中微子（orantineutrinos）质量的实验测定是一个缓慢且越来越复杂的过程。电子反中微子是最受青睐的对象。它们是在β衰变过程中产生的，同时电子也被发射出去。它们的性质通过基本守恒定律与逃逸中微子的自旋和质量直接相关。优选的β衰变源是氚，因为电子在β谱的端点处仅具有18.56KeV的能量。这是一个即使在meV分辨率下也可以在技术上实现的值。然而，人们正在处理β谱的端点，其中每eV能量间隔的电子通量的强度下降了10个数量级。这是所有旨在直接测定中微子质量的实验的核心问题。所有中微子静止质量实验都必须包括高分辨率的电子光谱仪;超低暗计数探测器，出色的校准程序，以及所有实验参数的超稳定性，以便长时间收集数据以科普统计不确定性。 得克萨斯大学奥斯汀分校的物理系正在与内布拉斯加大学、布兰代斯大学、密歇根理工大学、波莫纳学院和得克萨斯大学阿灵顿分校合作，进行一项新的努力。我们的方法是基于一系列的静电电子分析仪，这是为了记录β电子能量约1 eV的分辨率。其来源是30 K的气态分子氚。探测器很容易接近，可以屏蔽不必要的宇宙辐射，每天1个黑暗计数。 整个装置内部没有磁场。此外，我们将使用的气体电池作为电子衍射的目标，以校准的电压在光谱仪与布罗意波长的电子产生的远焦电子枪。这是可能的，因为T2的键长从拉曼光谱是非常公知的。束电子也将使我们的光谱仪功能达到约0.2 eV的分辨率。 总之，当所有装置按设计工作时，我们的实验将导致在0.5 eV水平上确定电子反中微子的质量。

The experimental determination of the mass of the neutrinos (orantineutrinos) is a slow and increasingly more complex process. The electron antineutrinos are the favored object. They are produced during beta-decay, and electrons are ejected at the same time. Their properties link directly to the spin and mass of the escaping neutrino through fundamental conservation laws. The preferred beta decay source is tritium since the electrons have only 18.56 KeV energy at the endpoint of the beta spectrum. This is a value, which is technologically achievable even with meV resolution. However one is dealing with the endpoint of the beta spectrum, where the intensities of the electron fluxes per eV energy interval are down by 10 order of magnitudes. This is the quintessential problem for all experiments aimed at the direct determination of the neutrino mass. All neutrino rest mass experiments must include electron spectrometers with high resolution; ultralow dark count detectors, excellent calibration procedures, and superstabilities for all experimental parameters to collect data for very long times to cope with the statistical uncertainties. A new effort is under way at the Physics Department of The University of Texas at Austin, in cooperation with the University of Nebraska, Brandeis University, Michigan Tech University, PomonaCollege, and The University of Texas at Arlington. Our approach is based on a series of electrostatic electron analyzers, which are designed to record the beta electron energies with about 1 eV resolution. The source is gaseous, molecular tritium at 30K. The detectors are easily accessible and can be shielded from unwanted cosmic radiation to 1 dark count per day. There is no magnetic field inside the whole apparatus. Furthermore we will use the gas cell as a target for electron diffraction in order to calibrate the voltages at the spectrometers with the de Broglie wavelenghts of electrons produced by a telefocus electron gun. This is possible since the bond length of T2 is very well known from Raman spectroscopy. The beam electrons will also give us laso the spectrometer function to about .2 eV resolution. In summary, when all units work as designed our experiment will lead to a determination of the mass of the elctron antineutrino at the .5 eV level.