Improved Search for Neutron to Mirror-Neutron Oscillations in the Presence of Mirror Magnetic Fields with a Dedicated Apparatus at the PSI UCN Source

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 (τnn′). 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 m3), 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 sensitivity to oscillation times τnn′/cos(β) well above a hundred seconds, with β 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.

Constraints on neutron–mirror-neutron oscillation from neutron star cooling

“…Therefore, the limit of nn 10 −17 eV can only be considered as an order of magnitude estimate, within a factor of few. This bound is particularly important, since currently planned terrestrial experiments are sensitive to nn at the level of 10 −17 eV [20][21][22][23][24][25][26][27][28][29]. However, it has been pointed out in our previous paper that there is a loophole in this argument [58], and the present paper is an elaboration of this result.…”

“…The current existing laboratory limits on n − n mixing are from Refs. [20][21][22][23][24][25][26][27][28][29]. The experimental results are conventionally presented in terms of the time scale τ nn .…”

“…Some of these experiments have observed anomalies up to 5σ , which could imply n −n oscillation with nn = (1÷2)×10 −17 eV [20,[23][24][25]. Therefore, experiment was designed to test these anomalies, which can exclude the value of nn down to 5 × 10 −18 eV for the range of δ nn up to few times 10 −11 eV [28]. The sensitivities can be further improved at the European Spallation Source [30] and other experiments [29].…”

Feebly-interacting particles: FIPs 2020 workshop report

“…The sensitivity in oscillation time of up to at least 400 s can be achieved. With the oscillation time and magnetic field sensitivities, HIBEAM can make order of magnitude improvements compared with other searches [1652,1659,1660].…”

Neutron-Mirror Neutron oscillations in Matter

“…These experiments still do not exclude the possibility of n − n oscillation time to be much less than the neutron decay time, and some of them even show anomalous deviations from null-hypothesis [39]. A new search is underway for testing these anomalies at the UCN facility of Paul Sherrer Insititute (PSI) [40].…”