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New High-Sensitivity Search for Neutron to Mirror-Neutron Oscillations at the PSI Ultracold Neutron Source

N. J. Ayres1, Z. Berezhiani2, G. Bison3, K. Bodek4, V. Bondar1, P.-J. Chiu1,3,*, M. Daum3, C. B. Doorenbos1,3, S. Emmenegger1 et al.

K. Kirch1,3, V. Kletzl1,3,†, J. Krempel1, B. Lauss3,‡, D. Pais1,3, I. Rienäcker3, D. Ries3, D. Rozpędzik4, P. Schmidt-Wellenburg3, K. S. Tanaka3,§, J. Zejma4, N. Ziehl1,∥, and G. Zsigmond3,¶

  • *Present address: Department of Physics, National Taiwan University, 106319 Taipei, Taiwan.
  • †Present address: Marietta-Blau-Institute for Particle Physics, Austrian Academy of Sciences, 1010 Vienna, Austria.
  • ‡Contact author: bernhard.lauss@psi.ch
  • §Present address: Waseda University, 3-4-1 Ookubo, Shinjuku-ku, Tokyo 169-8555, Japan.
  • ∥Contact author: ziehln@phys.ethz.ch
  • Contact author: geza.zsigmond@psi.ch
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Phys. Rev. Lett. 137, 051802 – Published 28 July, 2026

DOI: https://doi.org/10.1103/2qck-n6mb

Abstract

In a search for potential signals of neutron (n) to mirror-neutron (n′) oscillations, a collaboration centered at the Paul Scherrer Institute investigated the remaining parameter space claimed by anomalies with a dedicated high-sensitivity apparatus. An elaborate magnetic-field-mapping analysis and Monte Carlo simulation of the cumulative n−n′ oscillation probabilities along the neutron trajectories inside the storage vessel complemented the neutron data analysis. Magnetic fields were scanned in the range 5<B<109  μT. No evidence of anomalous neutron losses was found. Consequently, new limits for the n−n′ oscillation time constant were set. The parameter space, previously claimed for potential signals, has been excluded to 99.98%.

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Phys. Rev. Lett. 137, 051802– Published 28 July, 2026
  • Received 28 February 2026
  • Accepted 8 June 2026
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