# High-resolution and low-background $^{163}$Ho spectrum: interpretation of the resonance tails

Velte, C.; Ahrens, F.; Barth, A.; Blaum, K.; Braß, M.; Door, M.; Dorrer, H.; Düllmann, Ch E.; Eliseev, S.; Enss, C.; Filianin, P.; Fleischmann, A.; Gastaldo, L.; Goeggelmann, A.; Goodacre, T. Day; Haverkort, M. W.; Hengstler, D.; Jochum, J.; Johnston, K.; Keller, M.; ... mehr

##### Abstract:
The determination of the effective electron neutrino mass via kinematic analysis of beta and electron capture spectra is considered to be model-independent since it relies on energy and momentum conservation. At the same time the precise description of the expected spectrum goes beyond the simple phase space term. In particular for electron capture processes, many-body electron-electron interactions lead to additional structures besides the main resonances in calorimetrically measured spectra. A precise description of the $^{163}$Ho spectrum is fundamental for understanding the impact of low intensity structures at the endpoint region where a finite neutrino mass affects the shape most strongly. We present a low-background and high-energy resolution measurement of the $^{163}$Ho spectrum obtained in the framework of the ECHo experiment. We study the line shape of the main resonances and multiplets with intensities spanning three orders of magnitude. We discuss the need to introduce an asymmetric line shape contribution due to Auger–Meitner decay of states above the auto-ionisation threshold. With this we determine an enhancement of count rate at the endpoint region of about a factor of 2, which in turn leads to an equal reduction in the required exposure of the experiment to achieve a given sensitivity on the effective electron neutrino mass.

 Zugehörige Institution(en) am KIT Institut für Mikro- und Nanoelektronische Systeme (IMS) Publikationstyp Zeitschriftenaufsatz Publikationsmonat/-jahr 12.2019 Sprache Englisch Identifikator ISSN: 1434-6044, 1434-6052 KITopen-ID: 1000125027 Erschienen in The European physical journal / C Verlag Springer Band 79 Heft 12 Seiten Art. Nr.: 1026 Vorab online veröffentlicht am 21.12.2019 Nachgewiesen in Web of ScienceDimensionsScopus
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