A Search for Neutron to Mirror Neutron Oscillation Using Neutron Electric Dipole Moment Measurements

Abstract

Baryon number violation is a key ingredient of baryogenesis. It has been hypothesized that there could also be a parity-conjugated copy of the standard model particles, called mirror particles. The existence of such a mirror universe has specific testable implications, especially in the domain of neutral particle oscillation, viz. the baryon number violating neutron to mirror-neutron (n−n′) oscillation. Consequently, there were many experiments that have searched for n−n′ oscillation, and imposed constraints upon the parameters that describe it. Recently, further analysis on some of these results have identified anomalies which could point to the detection of n−n′ oscillation. All the previous efforts searched for n−n′ oscillation by comparing the relative number of ultracold neutrons that survive after a period of storage for one or both of the two cases: (i) comparison of zero applied magnetic field to a non-zero applied magnetic field, and (ii) comparison where the orientation of the applied magnetic field was reversed. However, n−n′ oscillations also lead to variations in the precession frequency of polarized neutrons upon flipping the direction of the applied magnetic field. Precession frequencies are measured, very precisely, by experiments searching for the electric dipole moment. For the first time, we used the data from the latest search for the neutron electric dipole moment to constrain n−n′ oscillation. After compensating for the systematic effects that affect the ratio of precession frequencies of ultracold neutrons and cohabiting 199Hg-atoms, chief among which was due to their motion in non-uniform magnetic field, we constrained any further perturbations due to n−n′ oscillation. We thereby provide a lower limit on the n−n′ oscillation time constant of τnn′/|cos(β)|>5.7s,0.36T′<B′<1.01T′ (95% C.L.), where β is the angle between the applied magnetic field and the ambient mirror magnetic field. This constraint is the best available in the range of 0.36T′<B′<0.40T′.

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 .…”

Ultracold neutron storage simulation using the Kassiopeia software package

“…We compared our simulation's results with three previously measured parameters associated with the precession chamber under consideration: the longitudinal relaxation time T 1 [39,42], the transverse relaxation time T 2 [40,42], and the effective trap lifetime τ including neutron decay and wall losses [41,42]. Using a similar simulation but with the converse of the process we have employed here, the parameters of η, V f and w associated with the trap could be obtained just by using the data of neutron storage loss as a function of storage time alone, as was done in reference [20,43]. Previous works neglected the effects of depolarization.…”

“…The mean time-of-flight, in turn, depends intimately on the time evolution of the energy spectra of the stored neutrons. A simple model involving a single loss-coefficient for the entire chamber was simulated using MCUCN to extract the energy evolution and thereby the mean time-of-flight of the stored neutrons in references [20,43]. Kassiopeia can further improve such simulations by performing realistic simulations of co-magnetometer atoms simultaneously with UCNs.…”