Determination of the electron neutrino rest mass via tritium decay

中微子(中微子)质量的实验测定是一个缓慢且日益复杂的过程。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，同时电子也会被抛出。它们的性质通过基本守恒定律与逃逸的中微子的自旋和质量直接相关。首选的衰减源是氚，因为电子在贝塔谱的终点处只有18.56keV的能量。这是一种价值，即使使用MEV分辨率在技术上也可以实现。然而，人们正在处理贝塔谱的终点，在这里，每EV能量区间的电子通量强度下降了10个数量级。对于所有旨在直接确定中微子质量的实验来说，这是一个典型的问题。所有中微子静止质量实验必须包括高分辨率的电子能谱仪、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，以便收集非常长时间的数据，以处理统计上的不确定因素。得克萨斯大学奥斯汀分校物理系正在与内布拉斯加州大学、布兰迪斯大学、密歇根理工大学、波莫纳学院和德克萨斯大学阿灵顿分校合作开展一项新的工作。我们的方法是基于一系列静电电子分析器，这些分析器被设计成以大约1 eV的分辨率记录β电子能量。在30K时，其来源是气态的分子氚。探测器很容易接近，可以屏蔽不必要的宇宙辐射，每天可达到1次暗计数。整个仪器内部没有磁场。此外，我们将使用气体室作为电子衍射的目标，以便用远焦电子枪产生的电子的德布罗意波长来校准光谱仪上的电压。这是可能的，因为从拉曼光谱可以很好地知道T2的键长。束流电子还将给我们提供激光光谱仪功能，分辨率约为0.2 eV。总而言之，当所有装置都按设计工作时，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.