  The observation of neutron to antineutron oscillation would be the first
experimental evidence to show that baryon number is not a conserved quantity.
It also provides an answer to the hypothesized post-sphaleron baryogenesis
mechanism shortly after the Big Bang. The free oscillation time
{\tau_{n\rightarrow\bar{n}} has a lower limit at 8.7 x 10^7 seconds determined
at ILL in 1994. Current beyond Standard Model theories of this oscillation time
estimate the value to be on the order of 10^{10} seconds. A new experiment is
proposed at the European Spallation Source that has 1000 times the sensitivity
of the previous experiment, and would confirm the viability of those beyond
Standard Model theories.
