Toward an improved search for neutron–antineutron oscillations

An observation of neutron–antineutron oscillations would constitute a discovery of fundamental importance for particle physics and cosmology. The required change in baryon number and lepton number (ΔB=2ΔB=2, ΔL=0ΔL=0) relates neutron–antineutron oscillations to neutrinoless double beta decay (ΔB=0ΔB=0, ΔL=2ΔL=2) and the physics of B–LB–L symmetry breaking and neutrino mass generation in several theories beyond the Standard Model which unify quarks and leptons. Recent theoretical models which posit new energy scales for B–L symmetry breaking in the ranges from 105105 to 1011GeV can produce neutron–antineutron oscillations close to the existing limits. We mention recent developments in cold and ultracold neutron technology which can make possible improvements in the sensitivity to the free neutron oscillation probability by factors from ≈100to1000. For these sensitivities a null result would place the most stringent limit on this possible mode of matter instability.