Coordination Funds

确定中微子质量的绝对尺度是当今粒子物理学的主要挑战之一。采用不同的方法实现了对亚电子伏特范围内中微子质量的灵敏度。其中，探索合适核素的β衰变和电子捕获过程的实验可以纯粹利用动量和能量守恒提供与模型无关的电子（反）中微子质量值信息。电子俘获163 Ho实验（ECHo）的目的是通过分析163 Ho电子俘获过程的量热测量能谱来研究亚电子伏特范围内的电子中微子质量。在ECHo实验中，将使用具有高能量分辨率和快速响应时间的低温金属磁量热计阵列，将163 Ho源嵌入吸收体中，以量热法测量EC谱。将使用彭宁阱质谱法对衰变能（QEC值）进行独立测量，目前不同的实验提供的值范围为2.3至2.8 keV。对于QEC测量以及163 Ho光谱的量热测量，将生产高纯度163 Ho源。为了提高量热测量的灵敏度，将对本底和降低本底的方法进行详细的研究。根据准备工作和目前正在进行的研发在ECHO的研究小组，我们建议建立一个DFG研究单位的目标，以实现所需的实验条件和知识，能够调查电子中微子质量在亚电子伏特范围内，并促进有关团体之间的合作。在该研究单元的范围内，我们建议开发和构建一个中等规模的实验，其特征在于1 kBq（ECHo-1 k）的活性，目的是通过对163 Ho EC谱的高精度、高统计量热测量来研究10 eV/c2以下范围内的电子中微子质量值。预期的结果将使电子中微子质量的极限比目前最严格的极限m（νe）< 225 eV/c2（95%CL）提高一个数量级以上。

The determination of the absolute scale of the neutrino masses is one of the major challenges of today’s particle physics. Different approaches are fol-lowed to achieve a sensitivity on neutrino masses in the sub-eV range. Among them, experiments exploring the beta decay and electron capture processes of suitable nuclides can provide model-independent information on the electron (anti)- neutrino mass value purely using momentum and ener-gy conservation. The Electron Capture 163Ho experiment, ECHo, is aimed at investigating the electron neutrino mass in the sub-eV range by means of the analysis of the calorimetrically measured energy spectrum following the elec-tron capture process of 163Ho. In the ECHo experiment, arrays of low tem-per-ature metallic magnetic calorimeters with high energy resolution and fast response time, having the 163Ho source embedded in the absorber, will be used to calorimetrically measure the EC spectrum. Independent measure-ments of the decay energy (QEC-value), for which different experiments cur-rently provide values ranging from 2.3 to 2.8 keV, will be performed using Penning-trap mass spectrometry. For the QEC measurements as well as for the calorimetric measurement of the 163Ho spectrum, high purity 163Ho sources will be produced. Detailed studies of the background and of meth-ods for its reduction will be carried out to increase the sensitivity of the calo-rimetric measurement. Based on the preparatory work and the presently on-going R&D in the research groups of ECHo we propose to establish a DFG Re-search Unit with the goal to achieve the required experimental conditions and the knowledge to be able to investigate the electron neutrino mass in the sub-eV range and to foster the collaboration between the groups involved. Within the scope of this Research Unit, we propose to develop and construct a medium-size experiment featuring an activity of 1 kBq (ECHo-1k) with the aim of investigating the value of the electron neutrino mass in the range be-low 10 eV/c2 by means of a high-precision, high-statistics calorimetric measure-ment of the 163Ho EC spectrum. The expected result will improve the limit on the electron neutrino mass by more than one order of magnitude with respect to the presently most stringent limit of m(νe) < 225 eV/c2 (95% CL).