Statistical sensitivity of the nEDM apparatus at PSI to neutron mirror-neutron oscillations

Abstract

The neutron and its hypothetical mirror counterpart, a sterile state degenerate in mass, could spontaneously mix in a process much faster than the neutron ${\hat{I}}^2$-decay. Two groups have performed a series of experiments in search of neutron - mirror-neutron ($n-n^{\prime }$) oscillations. They reported no evidence, thereby setting stringent limits on the oscillation time $\ddot{I}{„}_{n{n}^{\prime }}$. Later, these data sets have been further analyzed by Berezhiani et al.(2009-2017), and signals, compatible with $n-n^{\prime }$ oscillations in the presence of mirror magnetic fields, have been reported. The Neutron Electric Dipole Moment Collaboration based at the Paul Scherrer Institute performed a new series of experiments to further test these signals. In this paper, we describe and motivate our choice of run configurations with an optimal filling time of $29$s, storage times of $180$s and $380$s, and applied magnetic fields of $10\hat{I}¼$T and $20\hat{I}¼$T. The choice of these run configurations ensures a reliable overlap in settings with the previous efforts and also improves the sensitivity to test the signals. We also elaborate on the technique of normalizing the neutron counts, making such a counting experiment at the ultra-cold neutron source at the Paul Scherrer Institute possible. Furthermore, the magnetic field characterization to meet the requirements of this $n-n^{\prime }$ oscillation search is demonstrated. Finally, we show that this effort has a statistical sensitivity comparable to the current leading constraints for $n-n^{\prime }$ oscillations.

Proceedings of International Workshop on Particle Physics at Neutron Sources, PPNS-2018; May 24-26, 2018, LPSC, Grenoble, France; Abs. ID: 28 and 60. 10 Pages, 9 Figures