Abstract
The possibility that a neutron can be transformed to a hidden sector particle remains intriguingly open. Proposed theoretical models conjecture that the hidden sector can be represented by a mirror sector, and the neutron n can oscillate into its sterile mirror twin n′, exactly or nearly degenerate in mass with n. Oscillations n−n′ can take place in vacuum or in an environment containing regular matter and a magnetic field, in which only the neutron will be subject to interactions with the environment. We describe the propagation of the oscillating n−n′ system in a cold neutron beam passing through dense absorbing materials in connection to the possible regeneration type of experiments, where the effect of n→n′→n transformation can be observed.
Highlights
Current interest in the hidden sector in particle physics is motivated mostly by the apparent existence of Dark Matter (DM), which is not contained in the Standard Model (SM) and the nature of which is not yet determined
Since oscillations are suppressed inside the absorber, the system does not obtain the phase shift factor that would lead to the significant variation in the probability at the exit of the absorber, providing the state of the density matrix that is averaged and can serve as an initial condition for the propagation in vacuum behind the absorber
By computing the time evolution of the density matrix of the two-level system (n, n ) passing the environment where one of the components in the Hamiltonian is strongly interacting with an environment and another component is sterile, we provided the method for understanding the process of regeneration that can be used in experiments with cold neutron beams, e.g., in [47]
Summary
Current interest in the hidden sector in particle physics is motivated mostly by the apparent existence of Dark Matter (DM), which is not contained in the Standard Model (SM) and the nature of which is not yet determined. Regeneration experiments are promising for testing n − n oscillations in the case when the two states n and n have some small mass splitting of ∆m = mn − mn ∼ 100 neV or so This situation was used in [51] for explaining the neutron lifetime discrepancy between the trap and beam experiments. Such a small splitting between the ordinary and mirror particles can be obtained if mirror symmetry Z2 is very mildly broken, with the VEVs of two Higgses having a small difference, φ ≈ φ [52,53]. We think that the STEREO collaboration can benefit from our approach, in the region of larger ( /∆E) not shown in the paper [56] that might be relevant [51] for the neutron lifetime anomaly [57,58]
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