Improved limit on the effective electron neutrino mass with the ECHo-1k experiment
Abstract
The effective electron neutrino mass can be determined by analyzing the endpoint region of the 163Ho electron capture spectrum, provided a measurement with high energy resolution and high statistics using calorimetric techniques. Here, the Electron Capture in 163Ho collaboration, ECHo, presents an analysis of the most precise 163Ho spectrum currently available, obtained with the ECHo-1k experiment and comprising about 200 million events. A very low background rate of B=9.1(1.3)× 10-6 /eV/pixel/day was achieved allowing for a reliable analysis of the endpoint region. The derived endpoint energy Q = 2862(4) eV is in excellent agreement with the one independently determined via Penning-trap mass spectrometry of Q=2863.2(6) 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 m_e < 15 eV/c2 (90\% credible interval).
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