  Evidence for the ground state of the neutron-unbound nucleus 26O was observed
for the first time in the single proton-knockout reaction from a 82 MeV/u 27F
beam. Neutrons were measured in coincidence with 24O fragments. 26O was
determined to be unbound by 150+50-150 keV from the observation of low-energy
neutrons. This result agrees with recent shell model calculations based on
microscopic two- and three-nucleon forces.
