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New high-sensitivity search for neutron to mirror-neutron oscillations at the PSI UCN source

N. J. Ayres, Z. Berezhiani, G. Bison, K. Bodek, V. Bondar, P. -J. Chiu, M. Daum, C. B. Doorenbos, S. Emmenegger, K. Kirch, V. Kletzl, J. Krempel, B. Lauss, D. Pais, I. Rienäcker, D. Ries, D. Rozpedzik, P. Schmidt-Wellenburg, K. S. Tanaka, J. Zejma, N. Ziehl, G. Zsigmond

Abstract

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 %.

New high-sensitivity search for neutron to mirror-neutron oscillations at the PSI UCN source

Abstract

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 %.
Paper Structure (3 sections, 7 equations, 6 figures)

This paper contains 3 sections, 7 equations, 6 figures.

Table of Contents

  1. Supplemental Material
  2. Magnetic field mapper for the $n - n'$ experiment
  3. Calculations of the excluded solid angle ranges

Figures (6)

  • Figure 1: Cut through the schematic (CAD) experimental setup: (1) West-1 beamport shutter, (2) UCN guides, (3) horizontal guide shutter, (4) storage vessel, (5) butterfly shutter, (6) UCN detector, (7) magnetic field coils, (8) top lid of the storage vessel, (9) radiation shielding. Figure adapted from Ingo.
  • Figure 2: UCN counts during one storage measurement cycle (adapted from Ingo).
  • Figure 3: Mean asymmetry $\langle A_B \rangle$ as a function of target field $\textbf{B}$. The light grey line shows the limits of the null-hypothesis $H_0$ at the 95% C.L., the dark grey outline shows the same limit after correcting for the look-elsewhere-effect. $\langle A_B \rangle$ is consistent with $H_0$ within a standard error $\delta \langle A_B \rangle$.
  • Figure 4: The anomalous signal regions of Berezhiani-2018 Berezhiani:2017jkn from data in Ban:2007tp ($3\sigma$, red), Serebrov:2008her ($5.2\sigma$, blue) and Berezhiani:2017jkn ($2.5\sigma$, green) together with the 95% C.L. limits on $\tau_{nn'}/\sqrt{|\cos(b)|}$ from PSI-2009 Altarev:2009tg, PSI-2021 nEDM:2020ekj and this work as a function of the magnitude of the mirror-magnetic-field, $B'$. Along with the most conservative PSI-2025 limit (black line) excluding 99.98% of the full solid angle (4$\pi$), two higher limit curves but with less solid angle exclusion (99.62% and 89.84%) are plotted, corresponding to levels of factor 2 (dashed line) and 5 (dotted line) above the anomalous signals.
  • Figure 5: Picture of the mapper (see text) inside the electro-polished stainless steel UCN storage vessel.
  • ...and 1 more figures