Search for<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>n</mml:mi><mml:mo>−</mml:mo><mml:mrow><mml:mrow><mml:mover><mml:mrow><mml:mi>n</mml:mi></mml:mrow><mml:mrow><mml:mi>¯</mml:mi></mml:mrow></mml:mover></mml:mrow></mml:mrow></mml:math>Oscillation in Oxygen

This Letter reports the results of a search for neutron-antineutron transitions in oxygen, using a water Cherenkov detector of fiducial mass 3300 metric tons located 1570 m (water equivalent) underground. Two independent methods yield 90% -confidence lower limits of 1.7 \ifmmode\times\else\texttimes\fi{} ${10}^{31}$ and 2.4 \ifmmode\times\else\texttimes\fi{} ${10}^{31}$ yr, respectively, for the partial lifetime of this process. According to recent calculations the latter result corresponds to a lower limit in the range 2.7 \ifmmode\times\else\texttimes\fi{} ${10}^{7}$ to 1.1 \ifmmode\times\else\texttimes\fi{} ${10}^{8}$ sec for the free-neutron oscillation time.