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T: Fachverband Teilchenphysik

T 75: Neutrino physics without accelerators VI

T 75.5: Vortrag

Donnerstag, 2. April 2020, 17:35–17:50, H-HS XIII

ECHo - A ¹⁶³Ho spectrum and a bit of theory — •Clemens Velte for the ECHo collaboration — Kirchhoff Institute for Physics, Heidelberg University

The ECHo experiment belongs to the group of direct neutrino mass experiments and is designed to reach a sub-eV sensitivity via the analysis of the electron capture energy spectrum of ¹⁶³Ho. This analysis is considered to be model-independent since it only relies on energy and momentum conservation. At the same time the precise description of the expected spectrum goes beyond simple atomic models. In particular many-body electron-electron interactions lead to additional structures besides the main resonances in calorimetrically measured electron capture spectra. A precise description of the ¹⁶³Ho spectrum is fundamental to gain information on a sub-eV neutrino mass due to a change in the spectral shape. Especially the end point region is here of interest, since there the impact of a finite neutrino mass is the largest. We present a low background and high-energy resolution measurement of the ¹⁶³Ho spectrum and study the line shape of the main resonances and multiplets with intensities spanning three orders of magnitude. Furthermore we discuss the need to introduce an asymmetric line shape contribution (usually Lorentzian form) to improve the theoretical description of the experimental spectrum. With this, we predict an enhancement of count rate at the endpoint region of about a factor of 2, compared to previous theoretical models. This relaxes the constraints to reach a sub-eV sensitivity on the effective electron neutrino mass.