Improved search for neutron to mirror-neutron oscillations in the presence of mirror magnetic fields with a dedicated apparatus at the PSI UCN source

TL;DR

This paper presents a new experimental setup at PSI designed to detect neutron to mirror-neutron oscillations by measuring ultracold neutron loss under varying magnetic fields, aiming to explore previously untested parameter regions.

Contribution

The study introduces a large-volume UCN storage apparatus and demonstrates its capabilities, significantly expanding the sensitivity to mirror magnetic fields and oscillation times compared to previous experiments.

Findings

Demonstrated apparatus capabilities in 2020 test

Projected sensitivity to oscillation times above 100 seconds

Plan to scan magnetic fields to detect or exclude mirror-neutron signals

Abstract

While the international nEDM collaboration at the Paul Scherrer Institut (PSI) took data in 2017 that covered a considerable fraction of the parameter space of claimed potential signals of hypothetical neutron ($n$) to mirror-neutron ($n'$) transitions, it could not test all claimed signal regions at various mirror magnetic fields. Therefore, a new study of $n-n'$ oscillations using stored ultracold neutrons (UCNs)is underway at PSI, considerably expanding the reach in parameter space of mirror magnetic fields ($B'$) and oscillation time constants ($\tau_{nn'}$). The new apparatus is designed to test for the anomalous loss of stored ultracold neutrons as a function of an applied magnetic field. The experiment is distinguished from its predecessors by its very large storage vessel (1.47\,m$^3$), enhancing its statistical sensitivity. In a test experiment in 2020 we have demonstrated the capabilities of our apparatus. However, the full analysis of our recent data is still pending. Based on already demonstrated performance, we will reach a sensitivity to oscillation times $\tau_{nn'}/\sqrt{\cos(\beta)}$ well above hundred seconds, with $\beta$ being the angle between $B'$ and the applied magnetic field $B$. The scan of $B$ will allow the finding or the comprehensive exclusion of potential signals reported in the analysis of previous experiments and suggested to be consistent with neutron to mirror-neutron oscillations.