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

Abstract

Present probes do not exclude that the neutron ($n$) oscillation into mirror neutron ($n^{\prime }$), 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 ${\vec{B}}^{\prime }$ exists at the Earth, $n-n^{\prime }$ 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 ${\vec{B}}^{\prime }$. 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 $n-n^{\prime }$ oscillation in the presence of mirror magnetic field $B^{\prime }\sim 0.1$~G. Analyzing the experimental data on neutron loses, we obtain a new lower limit on $n-n^{\prime }$ oscillation time ${\tau }_{n{n}^{\prime }}>17$ s (95 % C.L.) for any $B^{\prime }$ between 0.08 and 0.17 G, and ${\tau }_{n{n}^{\prime }}/\sqrt{\cos \beta }>27$s (95 % C.L.) for any $B^{\prime }$ in the interval ($0.06÷0.25$) G.