Experimental search for neutron-antineutron transitions with free neutrons

Abstract The observation of neutron-antineutron transitions would be direct evidence for baryon number violation. For the first time an experiment has been carried out to search for this phenomenon with neutrons in free flight. The experiment using the research reactor at the Institut Laue-Langevin in Grenoble has set a lower limit to the oscillation time τ n n of 10 6 s.