Journal
PHYSICS REPORTS-REVIEW SECTION OF PHYSICS LETTERS
Volume 612, Issue -, Pages 1-45Publisher
ELSEVIER
DOI: 10.1016/j.physrep.2015.11.001
Keywords
Neutron-antineutron oscillation; Baryon number violation; Spallation; Cold neutron source; Quasi-free condition
Categories
Funding
- Indiana University Center for Spacetime Symmetries
- ORU Funding Program of the Office of Research of the University of Tennessee
- United States Department of Energy Office of High Energy Physics [DE-AC02-07CH11359]
- Division Of Physics
- Direct For Mathematical & Physical Scien [1316617, 1307426] Funding Source: National Science Foundation
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The observation of neutrons turning into antineutrons would constitute a discovery of fundamental importance for particle physics and cosmology. Observing the n-(n) over bar transition would show that baryon number (B) is violated by two units and that matter containing neutrons is unstable. It would provide a clue to how the matter in our universe might have evolved from the B = 0 early universe. If seen at rates observable in foreseeable next-generation experiments, it might well help us understand the observed baryon asymmetry of the universe. A demonstration of the violation of B-L by 2 units would have a profound impact on our understanding of phenomena beyond the Standard Model of particle physics. Slow neutrons have kinetic energies of a few meV. By exploiting new slow neutron sources and optics technology developed for materials research, an optimized search for oscillations using free neutrons from a slow neutron moderator could improve existing limits on the free oscillation probability by at least three orders of magnitude. Such an experiment would deliver a slow neutron beam through a magnetically-shielded vacuum chamber to a thin annihilation target surrounded by a low-background antineutron annihilation detector. Antineutron annihilation in a target downstream of a free neutron beam is such a spectacular experimental signature that an essentially background-free search is possible. An authentic positive signal can be extinguished by a very small change in the ambient magnetic field in such an experiment. It is also possible to improve the sensitivity of neutron oscillation searches in nuclei using large underground detectors built mainly to search for proton decay and detect neutrinos. This paper summarizes the relevant theoretical developments, outlines some ideas to improve experimental searches for free neutron oscillations, and suggests avenues both for theoretical investigation and for future improvement in the experimental sensitivity. (C) 2015 Elsevier B.V. All rights reserved.
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