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Mirror reflection could help search for neutron-antineutron oscillations

By 11th June 2019 June 30th, 2019 No Comments

Researchers at the Institut Laue-Langevin (ILL) have put forward a new experiment that could significantly increase the sensitivity of experiments searching for neutron-antineutron oscillations. The experiment could shed more light on why there is more matter than antimatter in the Universe. The work is published in Physical Review Letters.


Courtesy: Anna Nesvijevskaia

Best known as a world-class neutron-scattering facility that has made breakthroughs in condensed matter physics, materials science, chemistry and biology in recent years, the ILL also produces cold neutrons that are used to study fundamental problems in cosmology and particle physics.

In contrast to high-energy physics laboratories such as CERN that try to reproduce the conditions that were present less than a microsecond after the Big Bang, researchers at ILL look for the consequences of the Big Bang with a very high precision using such cold neutrons.

One of the topics they are studying is the oscillation of neutrons into antineutrons, a process that is forbidden by the Standard Model of particle physics because it would violate the law of conservation of baryon number. It is thus a very interesting testing ground to search for new physics.

Observing such an oscillation, even with a vanishingly small probability, would constitute a scientific discovery of fundamental importance for physics and cosmology, explains Valéry Nesvizhevsky, who led this research effort. Today’s Universe consists mainly of matter. With strictly conserved baryon number, the matter and antimatter, formed in equal quantities during the Big Bang, should have been annihilated.

The ILL researchers have now proposed a new method that could significantly increase the sensitivity of experiments searching for neutron-antineutron oscillations. The experiment is based on the ability of antineutrons to bounce off mirror surfaces thanks to a phenomenon called quantum reflection, which can occur if the velocity of the motion of these particles perpendicular to the surface is sufficiently small, says Valéry Nesvizhevsky. This property would allow researchers to build guides that can transport cold neutrons and antineutrons at the same time and would require more compact detectors and a length-scalable beamline compared to traditional free-flight experiments.

Read the research paper: Experimental Approach to Search for Free Neutron-Antineutron Oscillations Based on Coherent Neutron and Antineutron Mirror Reflection. V. V. Nesvizhevsky, V. Gudkov, K. V. Protasov, W. M. Snow, and A. Yu. Voronin. Phys. Rev. Lett10.1103/PhysRevLett.122.221802