Eur. Phys. J. C (2025) 85: 757
https://doi.org/10.1140/epjc/s10052-025-14354-z

Regular Article - Experimental Physics

Measurement of the inhomogeneity of the KATRIN tritium source electric potential by high-resolution spectroscopy of conversion electrons from $_{}^{\mathbf{83}\mathbf{m}}$Kr

¹ Department of Physics and Astronomy, University of North Carolina, 27599, Chapel Hill, NC, USA
² Institute for Astroparticle Physics (IAP), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
³ Institute for Data Processing and Electronics (IPE), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
⁴ Institute for Nuclear Physics, University of Münster, Wilhelm-Klemm-Str. 9, 48149, Münster, Germany
⁵ Istituto Nazionale di Fisica Nucleare (INFN)-Sezione di Milano-Bicocca, Piazza della Scienza 3, 20126, Milan, Italy
⁶ Politecnico di Milano, Dipartimento di Elettronica, Informazione e Bioingegneria, Piazza L. da Vinci 32, 20133, Milan, Italy
⁷ Istituto Nazionale di Fisica Nucleare (INFN)-Sezione di Milano, Via Celoria 16, 20133, Milan, Italy
⁸ Department of Physics, Faculty of Science, Chulalongkorn University, 10330, Bangkok, Thailand
⁹ Department of Physics, Carnegie Mellon University, 15213, Pittsburgh, PA, USA
¹⁰ Nuclear Physics Institute (NPI), Czech Academy of Sciences, 25068, Řež, Czech Republic
¹¹ Institute of Experimental Particle Physics (ETP), Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Str. 1, 76131, Karlsruhe, Germany
¹² TUM School of Natural Sciences, Physics Department, Technical University of Munich, James-Franck-Straße 1, 85748, Garching, Germany
¹³ Department of Physics, Faculty of Mathematics and Natural Sciences, University of Wuppertal, Gaußstr. 20, 42119, Wuppertal, Germany
¹⁴ Center for Experimental Nuclear Physics and Astrophysics, and Dept. of Physics, University of Washington, 98195, Seattle, WA, USA
¹⁵ Laboratory for Nuclear Science, Massachusetts Institute of Technology, 77 Massachusetts Ave, 02139, Cambridge, MA, USA
¹⁶ Dipartimento di Fisica, Università di Milano-Bicocca, Piazza della Scienza 3, 20126, Milan, Italy
¹⁷ Triangle Universities Nuclear Laboratory, 27708, Durham, NC, USA
¹⁸ Max Planck Institute for Physics, Boltzmannstr. 8, 85748, Garching, Germany
¹⁹ School of Physics and Center of Excellence in High Energy Physics and Astrophysics, Suranaree University of Technology, 30000, Nakhon Ratchasima, Thailand
²⁰ Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117, Heidelberg, Germany
²¹ IRFU (DPhP & APC), CEA, Université Paris-Saclay, 91191, Gif-sur-Yvette, France
²² Nuclear Science Division, Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
²³ Institute for Technical Physics (ITEP), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344, Eggenstein-Leopoldshafen, Germany
²⁴ Departamento de Química Física Aplicada, Universidad Autonoma de Madrid, Campus de Cantoblanco, 28049, Madrid, Spain
²⁵ Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, 12489, Berlin, Germany
²⁶ Institute for Theoretical Astrophysics, University of Heidelberg, Albert-Ueberle-Str. 2, 69120, Heidelberg, Germany
²⁷ Institut für Physik, Johannes-Gutenberg-Universität Mainz, 55099, Mainz, Germany
²⁸ Also affiliated with Department of Physics, Duke University, 27708, Durham, NC, USA
²⁹ Also affiliated with Department of Physics, Washington and Jefferson College, 15301, Washington, PA, USA
³⁰ Also affiliated with Oak Ridge National Laboratory, 37831, Oak Ridge, TN, USA
³¹ Institute for Nuclear Physics, University of Münster, Wilhelm-Klemm-Str. 9, 48149, Münster, Germany

^a m.boettcher@uni-muenster.de

Received: 18 March 2025
Accepted: 22 May 2025
Published online: 9 July 2025

Abstract

Precision spectroscopy of the electron spectrum of the tritium $\mathrm{\beta }$-decay near the kinematic endpoint is a direct method to determine the effective electron antineutrino mass. The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to determine this quantity with a sensitivity of better than $0.3\text{eV}$ ($90\%$ C.L.). An inhomogeneous electric potential in the tritium source of KATRIN can lead to distortions of the $\mathrm{\beta }$-spectrum, which directly impact the neutrino-mass observable. This effect can be quantified through precision spectroscopy of the conversion-electrons of co-circulated metastable $_{}^{83\text{m}}\text{Kr}$. Therefore, dedicated, several-weeks long measurement campaigns have been performed within the KATRIN data taking schedule. In this work, we infer the tritium source potential observables from these measurements, and present their implications for the neutrino-mass determination.