New experimental limits on neutron - mirror neutron oscillations in the presence of mirror magnetic field

TL;DR

This study sets new experimental lower limits on neutron to mirror neutron oscillation times, considering the influence of mirror magnetic fields, and investigates potential resonance effects affecting oscillation probabilities.

Contribution

The paper provides the first comprehensive experimental constraints on neutron-mirror neutron oscillations in the presence of mirror magnetic fields within a specific range.

Findings

Lower limit on oscillation time: >17 seconds at 95% C.L.

Oscillation time constraint: >27 seconds scaled by rac;1/\u221a{\u00b7}cosb2 for certain magnetic fields.

No evidence found for rapid neutron-mirror neutron oscillations under tested conditions.

Abstract

Present probes do not exclude that the neutron ($n$) oscillation into mirror neutron ($n'$), a sterile state exactly degenerate in mass with the neutron, can be a very fast process, in fact faster than the neutron decay itself. This process is sensitive to the magnetic field. Namely, if the mirror magnetic field $\vec{B}'$ exists at the Earth, $n-n'$ oscillation probability can be suppressed or resonantly amplified by the applied magnetic field $\vec{B}$, depending on its strength and on the angle $\beta$ between $\vec{B}$ and $\vec{B}'$. We present the results of ultra-cold neutron storage measurements aiming to check the anomalies observed in previous experiments which could be a signal for $n-n'$ oscillation in the presence of mirror magnetic field $B'\sim 0.1$~G. Analyzing the experimental data on neutron loses, we obtain a new lower limit on $n-n'$ oscillation time $\tau_{nn'} > 17$ s (95 % C.L.) for any $B'$ between 0.08 and 0.17 G, and $\tau_{nn'}/\sqrt{\cos\beta} > 27 $s (95 % C.L.) for any $B'$ in the interval ($0.06\div0.25$) G.