News from neutron-antineutron oscillations

An observation of oscillations of neutrons into antineutrons, occurring even with a vanishingly small probability, would violate the law of conservation of baryon number and would constitute a scientific discovery of fundamental importance for physics and cosmology. A strong hint that this law might be violated in Nature follows from the experimental fact that today's Universe consists mainly of matter: with strictly conserved baryon number, matter and antimatter, formed during the Big Bang in equal quantities, should have been annihilated. 

In a new paper, just published in PRL, the team proposes an experimental method that promises to largely increase the sensitivity of experiments searching for neutron-antineutron oscillations. It is based on the suggested ability of antineutrons, argued to follow from quantum mechanics, to bounce off mirror surfaces due to quantum reflection, if the component of the velocity of their motion perpendicular to the surface is sufficiently small. This property would allow to build guides able to transport cold neutrons and antineutrons simultaneously. Compared to free-flight experiments this would offer advantages of a more compact detector setup and a length-scalable beamline. 

Re.: Phys. Rev. Lett. 122, 221802 –7 June 2019.   DOI: 10.1103/PhysRevLett.122.221802

ILL instrument : the polarised cold neutron beam facility PF1B

Contact: Dr Valéry Nesvizhevsky, ILL