Experimental Approach to Search for Free Neutron-Antineutron Oscillations Based on Coherent Neutron and Antineutron Mirror Reflection

摘要

An observation of neutron-antineutron oscillations (n - (n) over bar), which violate both B and B - L conservation, would constitute a scientific discovery of fundamental importance to physics and cosmology. A stringent upper bound on its transition rate would make an important contribution to our understanding of the baryon asymmetry of the Universe by eliminating the postsphaleron baryogenesis scenario in the light quark sector. We show that one can design an experiment using slow neutrons that in principle can reach the required sensitivity of tau(n-(n) over bar) similar to 10(10) s in the oscillation time, an improvement of similar to 10(4) in the oscillation probability relative to the existing limit for free neutrons. The improved statistical accuracy needed to reach this sensitivity can be achieved by allowing both the neutron and antineutron components of the developing superposition state to coherently reflect from mirrors. We present a quantitative analysis of this scenario and show that, for sufficiently small transverse momenta of n/(n) over bar and for certain choices of nuclei for the n/(n) over bar guide material, the relative phase shift of the n and (n) over bar components upon reflection and the (n) over bar annihilation rate can be small enough to maintain sufficient coherence to benefit from the greater phase space acceptance the mirror provides.