https://doi.org/10.1140/epjc/s10052-021-09325-z
Regular Article - Experimental Physics
Precision measurement of the electron energy-loss function in tritium and deuterium gas for the KATRIN experiment
1
Tritium Laboratory Karlsruhe (TLK), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
2
Institute for Data Processing and Electronics (IPE), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
3
Institute for Astroparticle Physics (IAP), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
4
Institute of Experimental Particle Physics (ETP), Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Str. 1, 76131, Karlsruhe, Germany
5
Institute for Nuclear Research of Russian Academy of Sciences, 60th October Anniversary Prospect 7a, 117312, Moscow, Russia
6
Institut für Kernphysik, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Str. 9, 48149, Münster, Germany
7
Technische Universität München, James-Franck-Str. 1, 85748, Garching, Germany
8
Max-Planck-Institut für Physik, Föhringer Ring 6, 80805, Munich, Germany
9
Department of Physics and Astronomy, University of North Carolina, 27599, Chapel Hill, NC, USA
10
Triangle Universities Nuclear Laboratory, 27708, Durham, NC, USA
11
Institute for Nuclear and Particle Astrophysics and Nuclear Science Division, Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
12
Department of Physics, Faculty of Mathematics and Natural Sciences, University of Wuppertal, Gaußstr. 20, 42119, Wuppertal, Germany
13
Departamento de Química Física Aplicada, Universidad Autonoma de Madrid, Campus de Cantoblanco, 28049, Madrid, Spain
14
Center for Experimental Nuclear Physics and Astrophysics, and Dept. of Physics, University of Washington, 98195, Seattle, WA, USA
15
Nuclear Physics Institute of the CAS, v. v. i., 250 68, Řež, Czech Republic
16
Laboratory for Nuclear Science, Massachusetts Institute of Technology, 77 Massachusetts Ave, 02139, Cambridge, MA, USA
17
Department of Physics, Carnegie Mellon University, 15213, Pittsburgh, PA, USA
18
IRFU (DPhP & APC), CEA, Université Paris-Saclay, 91191, Gif-sur-Yvette, France
19
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117, Heidelberg, Germany
20
Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489, Berlin, Germany
Received:
19
May
2021
Accepted:
8
June
2021
Published online:
5
July
2021
The KATRIN experiment is designed for a direct and model-independent determination of the effective electron anti-neutrino mass via a high-precision measurement of the tritium 
-decay endpoint region with a sensitivity on 
of 0.2 
(90% CL). For this purpose, the -electrons from a high-luminosity windowless gaseous tritium source traversing an electrostatic retarding spectrometer are counted to obtain an integral spectrum around the endpoint energy of 18.6 keV. A dominant systematic effect of the response of the experimental setup is the energy loss of -electrons from elastic and inelastic scattering off tritium molecules within the source. We determined the energy-loss function in-situ with a pulsed angular-selective and monoenergetic photoelectron source at various tritium-source densities. The data was recorded in integral and differential modes; the latter was achieved by using a novel time-of-flight technique. We developed a semi-empirical parametrization for the energy-loss function for the scattering of 18.6-keV electrons from hydrogen isotopologs. This model was fit to measurement data with a 95% 
gas mixture at 30 K, as used in the first KATRIN neutrino-mass analyses, as well as a 
gas mixture of 96% purity used in KATRIN commissioning runs. The achieved precision on the energy-loss function has abated the corresponding uncertainty of 
[1] in the KATRIN neutrino-mass measurement to a subdominant level.
© The Author(s) 2021
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Funded by SCOAP3
