Precision measurement of the electron energy-loss function in tritium and deuterium gas for the KATRIN experiment
Authors: Aker M. , Beglarian A. , Behrens J. , Berlev A. , Besserer U. , Bieringer B. , Block F. , Bornschein B. , Bornschein L. , Böttcher M. , Brunst T. , Caldwell T. S. , Carney R. M. D. , Chilingaryan S. , Choi W. , Debowski K. , Deffert M. , Descher M. , Barrero D. Díaz , Doe P. J. , Dragoun O. , Drexlin G. , Edzards F. , Eitel K. , Ellinger E. , Miniawy A. El , Engel R. , Enomoto S. , Felden A. , Formaggio J. A. , Fränkle F. M. , Franklin G. B. , Friedel F. , Fulst A. , Gauda K. , Gil W. , Glück F. , Groh S. , Grössle R. , Gumbsheimer R. , Hannen V. , Haußmann N. , Heizmann F. , Helbing K. , Hickford S. , Hiller R. , Hillesheimer D. , Hinz D. , Höhn T. , Houdy T. , Huber A. , Jansen A. , Karl C. , Kellerer J. , Kleesiek M. , Klein M. , Köhler C. , Köllenberger L. , Kopmann A. , Korzeczek M. , Kovalík A. , Krasch B. , Krause H. , Kunka N. , Lasserre T. , La Cascio L. , Lebeda O. , Lehnert B. , Le T. L. , Lokhov A. , Machatschek M. , Malcherek E. , Mark M. , Marsteller A. , Martin E. L. , Meier M. , Melzer C. , Menshikov A. , Mertens S. , Mostafa J. , Müller K. , Niemes S. , Oelpmann P. , Parno D. S. , Poon A. W. P. , Poyato J. M. L. , Priester F. , Ranitzsch P. C.-O. , Robertson R. G. H. , Rodejohann W. , Rodenbeck C. , Röllig M. , Röttele C. , Ryšavý M. , Sack R. , Saenz A. , Schäfer P. , Schaller A. , Schimpf L. , Schlösser K. , Schlösser M. , Schlüter L. , Schneidewind S. , Schrank M. , Schulz B. , Schwachtgen C. , Šefčík M. , Seitz-Moskaliuk H. , Sibille V. , Siegmann D. , Slezák M. , Steidl M. , Sturm M. , Sun M. , Tcherniakhovski D. , Telle H. H. , Thorne L. A. , Thümmler T. , Titov N. , Tkachev I. , Trost N. , Urban K. , Valerius K. , Vénos D. , Hernández A. P. Vizcaya , Weinheimer C. , Welte S. , Wendel J. , Wilkerson J. F. , Wolf J. , Wüstling S. , Xu W. , Yen Y.-R. , Zadoroghny S. , Zeller G. 
Published: 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 $$\upbeta $$
β
-decay endpoint region with a sensitivity on $$m_\nu $$

m
ν

of 0.2 $$\hbox {eV}/\hbox {c}^2$$

eV
/

c
2

(90% CL). For this purpose, the $$\upbeta $$
β
-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 $$\upbeta $$
β
-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% $$\hbox {T}_2$$

T
2

gas mixture at 30 K, as used in the first KATRIN neutrino-mass analyses, as well as a $$\hbox {D}_2$$

D
2

gas mixture of 96% purity used in KATRIN commissioning runs. The achieved precision on the energy-loss function has abated the corresponding uncertainty of $$\sigma (m_\nu ^2)< {{10}^{-2}}{\hbox {eV}^{2}}$$

σ

(

m
ν
2

)

<

10

-
2

eV
2

[1] in the KATRIN neutrino-mass measurement to a subdominant level.