New Search for Mirror Neutrons at HFIR (1710.00767v2)

Abstract: The theory of mirror matter predicts a hidden sector made up of a copy of the Standard Model particles and interactions but with opposite parity. If mirror matter interacts with ordinary matter, there could be experimentally accessible implications in the form of neutral particle oscillations. Direct searches for neutron oscillations into mirror neutrons in a controlled magnetic field have previously been performed using ultracold neutrons in storage/disappearance measurements, with some inconclusive results consistent with characteristic oscillation time of $\tau$$\sim$10~s. Here we describe a proposed disappearance and regeneration experiment in which the neutron oscillates to and from a mirror neutron state. An experiment performed using the existing General Purpose-Small Angle Neutron Scattering instrument at the High Flux Isotope Reactor at Oak Ridge National Laboratory could have the sensitivity to exclude up to $\tau$$<$15~s in 1 week of beamtime and at low cost.

• The paper proposes a novel cold neutron experiment at HFIR to search for oscillations into mirror neutron states, exploring the mirror matter hypothesis.
• Leveraging HFIR's capabilities, the experiment involves disappearance and regeneration stages designed to probe oscillation times up to 15 seconds using cold neutrons.
• Confirmation of mirror neutron oscillations would indicate physics beyond the Standard Model with significant implications for dark matter theories.

Review of "New Search for Mirror Neutrons at HFIR"

The paper "New Search for Mirror Neutrons at HFIR" presents an experimental proposal exploring the hypothesis of mirror matter, a potential dark matter candidate, through neutron oscillations. This intriguing proposition postulates a hidden sector paralleling the Standard Model, engendering implications for neutral particle oscillations — notably those involving neutrons that transition to mirror neutron states and vice versa.

Theoretical interest in mirror matter has surfaced periodically over recent decades, driven by ongoing challenges in explaining dark matter phenomena exclusively through gravitational interactions. Mirror matter assumes parity and time-reversal symmetries as its core postulation, which could theoretically initiate observable oscillatory phenomena in a controlled environment.

Experimental Focus and Proposal

The authors describe a regeneration and disappearance experiment leveraging the facilities at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory. Unlike prior investigations using ultracold neutrons, this experiment opts for cold neutrons, potentially allowing the probing of smaller oscillation times in the range up to 15 seconds if successful.

This contributes practical advancement; HFIR's existing infrastructure facilitates a low-cost, high-throughput experimental program given its efficient neutron production. The proposal embraces dual-stage experimentation:

1. Disappearance Stage: This phase involves a finely-tuned magnetic field control to induce and detect changes in the cold neutron flux, indicating transitions to a mirror state.
2. Regeneration Stage: Following disappearance, the regeneration stage captures neutrons oscillating back from the mirror state through a distinctly structured magnetic and detection field setup.

The novel utilization of the GP-SANS instrument's capabilities enhances the experimental validity by potentially yielding results within a week of beamtime by providing a detection method for validating any observed oscillations.

Numerical Results and Implications

The proposed experimental setup is impressive in its ambition to exclude oscillation times of less than 15 seconds over diverse magnetic field strengths (-125 mG to 125 mG). This approach offers an opportunity to resolve discrepancies and extend previous ultracold neutron research, which had detected possible oscillation signals with a moderate degree of statistical significance.

Certainly, this exploration holds broad theoretical implications. Experimental confirmation of neutron oscillations into mirror states would suggest the presence of a novel class of interactions beyond the Standard Model, enriching the landscape of particle physics with profound reverberations for dark matter theories.

Future Directions

The paper envisions further experiments at HFIR, intending to leverage the proven infrastructure and streamline capabilities for high sensitivity detection. Future work could adapt the proposed methodologies for broader parameter spaces, enhancing potential signal detection far beyond present capabilities.

Overall, this paper exemplifies a collaborative effort across multiple institutions to refine cold neutron experimentation into fundamental physics inquiries. The exploration of mirror matter through neutron oscillations could illuminate cornerstones in hidden sector physics and dark matter interactions, meriting further theoretical and experimental scrutiny.

In conclusion, while the empirical realization of this experiment is integral, the endeavor harmonizes a conceptual scaffold for next-generation particle physics initiatives aiming to discern the elusive properties of dark matter.