用中子电偶极矩测量研究中子-镜像中子振荡
A search for neutron to mirror neutron oscillation using neutron electric dipole moment measurements
摘要：
重子数破缺是重子发生的关键因素。有人假设，也可能有一个宇称共轭副本的标准模型粒子，称为镜像粒子。这种镜像宇宙的存在具有特殊的可检验意义，特别是在中性粒子振荡领域，即重子数破坏中子到镜像中子（$n-n'$）振荡。因此，有许多实验都在寻找$n-n'$振荡，并对描述它的参数施加了限制。所有以前的努力都是通过比较两种情况中的一种或两种情况下储存一段时间后存活的超冷中子的相对数量来寻找$n-n'$振荡的：（i）零施加的磁场与非零施加的磁场的比较，以及（ii）施加的磁场的方向被反转的比较。然而，当翻转所施加的磁场的方向时，$n-n'$振荡也导致极化中子的进动频率的变化。我们第一次使用了中子电偶极矩的最新搜索数据[Phys. Rev. Lett. 124，081803（2020）]以限制$n-n'$振荡。在补偿了影响超冷中子和共存$^{199}$ Hg原子的进动频率比的系统效应之后，我们限制了由于$n-n'$振荡而引起的任何进一步的扰动。因此，我们提供了一个$n-n'$振荡时间常数的下限，即$τ_{nn'}/\sqrt{|\cos(β)|} > 5.7~$ s，$0.36~μ$ T' $<B'<1.01~μ$ T'（95\% C.L.），其中，$β$是所施加的磁场与环境镜磁场之间的角度。该约束是$0.36~μ$ T“$<B'<0.40~μ$ T”范围内的最佳可用约束。
英文摘要：
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. 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. For the first time, we used the data from the latest search for the neutron electric dipole moment [Phys. Rev. Lett. 124, 081803 (2020)] to constrain $n-n'$ oscillation. After compensating for the systematic effects that affect the ratio of precession frequencies of ultracold neutrons and cohabiting $^{199}$Hg-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 $τ_{nn'}/\sqrt{|\cos(β)|} > 5.7~$s, $0.36~μ$T'$<B'<1.01~μ$T' (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 $0.36~μ$T'$<B'<0.40~μ$T'.
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