In a search for potential signals of neutron (n) to mirror-neutron (n') oscillations, a collaboration centered at the Paul Scherrer Institute (PSI) 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 microT < B < 109 microT. 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 %.
@article{arxiv.2602.23487,
title = {New high-sensitivity search for neutron to mirror-neutron oscillations at the PSI UCN source},
author = {N. J. Ayres and Z. Berezhiani and G. Bison and K. Bodek and V. Bondar and P. -J. Chiu and M. Daum and C. B. Doorenbos and S. Emmenegger and K. Kirch and V. Kletzl and J. Krempel and B. Lauss and D. Pais and I. Rienäcker and D. Ries and D. Rozpedzik and P. Schmidt-Wellenburg and K. S. Tanaka and J. Zejma and N. Ziehl and G. Zsigmond},
journal= {arXiv preprint arXiv:2602.23487},
year = {2026}
}