Search for an interaction mediated by axion-like particles with ultracold neutrons at the PSI

N. J. Ayres, G. Bison, K. Bodek, V. Bondar, T. Bouillaud, E. Chanel, P. J. Chiu, B. Clement, C. B. Crawford, M. Daum, C. B. Doorenbos, S. Emmenegger, M. Fertl, P. Flaux, W. C. Griffith, P. G. Harris, N. Hild, M. Kasprzak, K. Kirch, V. KletzlP. A. Koss, J. Krempel, B. Lauss, T. Lefort, P. Mohanmurthy, O. Naviliat-Cuncic, D. Pais, F. M. Piegsa, G. Pignol, M. Rawlik, I. Rienäcker, D. Ries, S. Roccia, D. Rozpedzik, P. Schmidt-Wellenburg, N. Severijns, B. Shen, K. Svirina, R. Tavakoli Dinani, J. A. Thorne, S. Touati, A. Weis, E. Wursten, N. Yazdandoost, J. Zejma, N. Ziehl, G. Zsigmond

Research output: Contribution to journalArticlepeer-review


We report on a search for a new, short-range, spin-dependent interaction using a modified version of the experimental apparatus used to measure the permanent neutron electric dipole moment at the Paul Scherrer Institute. This interaction, which could be mediated by axion-like particles, concerned the unpolarized nucleons (protons and neutrons) near the material surfaces of the apparatus and polarized ultracold neutrons stored in vacuum. The dominant systematic uncertainty resulting from magnetic-field gradients was controlled to an unprecedented level of approximately 4 pT cm−1 using an array of optically-pumped cesium vapor magnetometers and magnetic-field maps independently recorded using a dedicated measurement device. No signature of a theoretically predicted new interaction was found, and we set a new limit on the product of the scalar and the pseudoscalar couplings g s g p λ 2 < 8.3 × 10 − 28 m2 (95% C.L.) in a range of 5 µm < λ < 25 mm for the monopole-dipole interaction. This new result confirms and improves our previous limit by a factor of 2.7 and provides the current tightest limit obtained with free neutrons.

Original languageEnglish
Article number103012
JournalNew Journal of Physics
Issue number10
StatePublished - Oct 2023

Bibliographical note

Publisher Copyright:
© 2023 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft.


  • axion
  • axion-like particle
  • beyond Standard Model physics
  • dark matter

ASJC Scopus subject areas

  • General Physics and Astronomy


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