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Ultracold Neutron Energy Spectrum and Storage Properties from Magnetically Induced Spin Depolarization

N. J. Ayres1, G. Ban2, G. Bison3, K. Bodek4, V. Bondar1, T. Bouillaud5, D. Bowles6, G. L. Caratsch1,3, E. Chanel7,* et al. (nEDM Collaboration at PSI)

E. Chanel7,*, W. Chen1,3, P.-J. Chiu1,3,†, C. B. Crawford6, V. Czamler5, M. Daum3, C. B. Doorenbos1,3, M. Ferry5, M. Fertl8, A. Fratangelo7, D. Galbinski2, W. C. Griffith9, Z. D. Grujic10, K. Kirch1,3, V. Kletzl1,3,‡, B. Lauss3, T. Lefort2, A. Lejuez2, R. Li11, K. Michielsen5, J. Micko7, P. Mullan1, A. Mullins6, O. Naviliat-Cuncic2, D. Pais1,3, F. M. Piegsa7, G. Pignol5, C. Pistillo7, D. Rebreyend5, I. Rienäcker1,3, D. Ries3, S. Roccia5, D. Rozpedzik4, W. Saenz-Arevalo2, L. Sanchez-Real Zielniewicz1, P. Schmidt-Wellenburg3, E. P. Segarra3,1,§, L. Segner1, N. Severijns11, K. Svirina5,∥, K. S. Tanaka3,¶, J. Thorne7,1, J. Vankeirsbilck11, N. von Schickh1,3, N. Yazdandoost3, J. Zejma4, N. Ziehl1, and G. Zsigmond3 (nEDM Collaboration at PSI)

  • 1Institute for Particle Physics and Astrophysics, ETH Zürich, CH-8093 Zurich, Switzerland
  • 2Normandie Université, ENSICAEN, UNICAEN, CNRS/IN2P3, LPC Caen, 14000 Caen, France
  • 3Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
  • 4Marian Smoluchowski Institute of Physics, Jagiellonian University, 30-348 Cracow, Poland
  • 5Université Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, 38026 Grenoble, France
  • 6Department of Physics and Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA
  • 7Laboratory for High Energy Physics and Albert Einstein Center for Fundamental Physics, University of Bern, CH-3012 Bern, Switzerland
  • 8Institute of Physics, Johannes Gutenberg University, D-55128 Mainz, Germany
  • 9Department of Physics and Astronomy, University of Sussex, Falmer, Brighton BN1 9QH, United Kingdom
  • 10Institute of Physics, Photonics Center, University of Belgrade, 11080 Belgrade, Serbia
  • 11Instituut voor Kern- en Stralingsfysica, University of Leuven, B-3001 Leuven, Belgium

  • *Present address: Institut Laue-Langevin, 71 avenue des Martyrs CS 20156, 38042 GRENOBLE Cedex 9, France.
  • †Present address: National Taiwan University, 106319 Taipei, Taiwan.
  • ‡Present address: Marietta Blau Institute for Particle Physics, Austrian Academy of Sciences, 1010 Vienna, Austria.
  • §Contact author: efrain.segarra@psi.ch
  • ∥Present address: Institut Laue–Langevin, CS 20156, 38042 Grenoble Cedex 9, France and Physikalisches Institut, Universitat Heidelberg, Im Neuenheimer Feld 226, 69120 Heidelberg, Germany.
  • Present address: Waseda University, Tokyo 169-8555, Japan.
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Phys. Rev. Lett. 136, 221902 – Published 5 June, 2026

DOI: https://doi.org/10.1103/hspm-dwkn

Abstract

We present a novel method for extracting the energy spectrum of ultracold neutrons from magnetically induced spin depolarization measurements using the n2EDM apparatus. This method is also used to exploit sensitivity to the storage properties of the materials used to trap ultracold neutrons, specifically, whether collisions are specular or diffuse. To do so, we utilize tomat simulation to map storage properties to correlation times of the ultracold neutrons to induced magnetic nonuniformities. We highlight the sensitivity of this new technique by comparing the two different storage chambers of the n2EDM experiment, which host different ultracold neutron energy spectra. This method should prove to be invaluable to assess systematic effects in experiments utilizing spin-polarized systems with precise magnetic control and long spin-spin coherence time relative to the observation time, such as neutron electric dipole moment and neutron lifetime experiments worldwide.

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Phys. Rev. Lett. 136, 221902– Published 5 June, 2026
  • Received 10 November 2025
  • Revised 30 January 2026
  • Accepted 14 April 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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