Bonn 2020 – scientific programme
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T: Fachverband Teilchenphysik
T 75: Neutrino physics without accelerators VI
T 75.7: Talk
Thursday, April 2, 2020, 18:05–18:20, H-HS XIII
Measurement of the Low Energy Electron Capture Spectrum of 163Ho — •Robert Hammann for the ECHo collaboration — Kirchhoff-Institute for Physics, Heidelberg University, Germany
The aim of the electron capture in 163Ho experiment (ECHo) is to directly measure the effective electron neutrino mass with sub-eV sensitivity by analysing the weak decay of 163Ho. For this purpose, a high statistics and high energy resolution measurement of the electron capture spectrum is required. This can be achieved using arrays of metallic magnetic calorimeters with 163Ho enclosed in the absorber operated at millikelvin temperatures.
In this contribution we present a calorimetric measurement of the spectrum with the 64 pixel ECHo-1k chip. Three detectors had an outstandingly low readout noise, which allowed for a very low threshold. With these detectors a total of 5.4·106 163Ho decay events were acquired in the energy range from 15 eV to 2800 eV with an energy resolution of 4.5 eV at the NI-line with 411 eV in the final spectrum.
Thanks to the low threshold as well as an improved algorithm used for data reduction, it was possible to resolve the low energy part of the spectrum with unprecedented detail. In particular, the OII-line was observed for the first time with a resonance energy of about 27 eV. Furthermore, features of the OI-line related to higher order atomic transitions similar to those found for the NI-line were observed.
These results are essential for the development of a precise description of the theoretical 163Ho spectrum over the full energy range.