  A sensitive search for neutron-antineutron oscillations can provide a unique
probe of some of the central questions in particle physics and cosmology: the
energy scale and mechanism for baryon number violation, the origin of the
baryon-antibaryon asymmetry of the universe, and the mechanism for neutrino
mass generation. A remarkable opportunity has emerged to search for such
oscillations with the construction of the European Spallation Source (ESS). A
collaboration has been formed which has proposed a search at the ESS, which
would provide a sensitivity to the oscillation probability which is three
orders of magnitude greater than that achieved at an ILL experiment at which
the present best limit on free neutron-antineutron oscillations was obtained.
