Sprecher
Beschreibung
The effective electron neutrino mass can be derived from the analysis of the endpoint region of electron capture spectra, since the finite mass distorts the spectral shape near the Q value. In ECHo the shape of the Ho-163 electron capture spectrum is studied. During the first phase of the ECHo experiment, more than 200 million Ho-163 events were acquired using 2 arrays of metallic magnetic calorimeters enclosing Ho-163. For a reliable analysis of the endpoint region, a precise calibration of the spectrum was obtained by applying a tailored procedure determined in a dedicated calibration measurement. Since theoretical models fail to provide an accurate analytical description of the spectral shape, we have tested two different approaches for the determination of a phenomenological function. The obtained functions were tested for stability of fit in the endpoint region of the acquired Ho-163 spectrum. We present the analysis of the ECHo-1k data leading to the present best limit of 15 eV (90%) credibility interval (18 eV 95% C.I.) and discuss the study of systematic uncertainties.