Abstract:
The effective electron neutrino mass can be determined by analyzing the endpoint region of the 
Ho electron capture spectrum, provided a measurement with high energy resolution and high statistics using calorimetric techniques. Here, the Electron Capture in Ho collaboration, ECHo, presents an analysis of the most precise Ho spectrum currently available, obtained with the ECHo-1k experiment and comprising about 200 million events. A very low background rate of 
/eV/pixel/day was achieved allowing for a reliable analysis of the endpoint region. The derived endpoint energy 
eV is in excellent agreement with the one independently determined via Penning-trap mass spectrometry of eV [1]. The upper limit of the effective electron neutrino mass is improved by almost a factor 2 compared to the lowest current value [2], reaching 
eV/c 
(90\% credible interval).
F. Adam, F. Ahrens, L. E. A. Perez, M. W. Haverkort, K. Blaum et al., „Improved limit on
the effective electron neutrino mass with the ECHo-1k experiment“, 3. Sep. 2025, arXiv:2509.03423 (2025).
https://arxiv.org/abs/2509.03423
Related to Project B01