A test of $\Delta $B=2 baryon number nonconservation. MOHAPATRA 1980 and MOHAPATRA 1989 discuss the theoretical motivations for looking for ${{\mathit n}}{{\overline{\mathit n}}}$ oscillations. DOVER 1983 and DOVER 1985 give phenomenological analyses. The best limits come from looking for the decay of neutrons bound in nuclei. However, these analyses require model-dependent corrections for nuclear effects. See KABIR 1983 , DOVER 1989 , ALBERICO 1991 , and GAL 2000 for discussions. Direct searches for ${{\mathit n}}$ $\rightarrow$ ${{\overline{\mathit n}}}$ transitions using reactor neutrons are cleaner but give somewhat poorer limits. We include limits for both free and bound neutrons in the Summary Table. See MOHAPATRA 2009 and PHILLIPS 2016 for recent reviews.

VALUE (s) CL% DOCUMENT ID TECN  COMMENT $\bf{>4.7 \times 10^{8}}$ 90 1 ABE 2021 CNTR ${{\mathit n}}$ bound in oxygen $\bf{>8.6 \times 10^{7}}$ 90 BALDO-CEOLIN 1994 CNTR Reactor (free) neutrons • • We do not use the following data for averages, fits, limits, etc. • • $>1.37 \times 10^{8}$ 90 2 AHARMIM 2017 SNO ${{\mathit n}}$ bound in deuteron $>2.7 \times 10^{8}$ 90 ABE 2015 C CNTR ${{\mathit n}}$ bound in oxygen $>1.3 \times 10^{8}$ 90 CHUNG 2002 B SOU2 ${{\mathit n}}$ bound in iron $>1 \times 10^{7}$ 90 BALDO-CEOLIN 1990 CNTR See BALDO-CEOLIN 1994 $>1.2 \times 10^{8}$ 90 BERGER 1990 FREJ ${{\mathit n}}$ bound in iron $>4.9 \times 10^{5}$ 90 BRESSI 1990 CNTR Reactor neutrons $>4.7 \times 10^{5}$ 90 BRESSI 1989 CNTR See BRESSI 1990 $>1.2 \times 10^{8}$ 90 TAKITA 1986 CNTR ${{\mathit n}}$ bound in oxygen $>1 \times 10^{6}$ 90 FIDECARO 1985 CNTR Reactor neutrons $>8.8 \times 10^{7}$ 90 PARK 1985 B CNTR $>3 \times 10^{7}$ BATTISTONI 1984 NUSX $> 0.27 - 1.1 \times 10^{8}$ JONES 1984 CNTR $>2 \times 10^{7}$ CHERRY 1983 CNTR 1  ABE 2021 supersedes ABE 2015C. 2  The AHARMIM 2017 value is an unbounded limit (it does not assume a positive lifetime). The bounded limit is $1.23 \times 10^{8}$ sec.

References:

ABE 2021 PR D103 012008 Neutron-antineutron oscillation search using a 0.37 megaton-years exposure of Super-Kamiokande AHARMIM 2017 PR D96 092005 Search for Neutron-Antineutron Oscillations at the Sudbury Neutrino Observatory ABE 2015C PR D91 072006 The Search for ${{\mathit n}}−{{\overline{\mathit n}}}$ Oscillation in Super-Kamiokande I CHUNG 2002B PR D66 032004 Search for Neutron Antineutron Oscillations using Multiprong Events in Soudan-2 BALDO-CEOLIN 1994 ZPHY C63 409 A New Experimental Limit on Neutron Antineutron Oscillations BALDO-CEOLIN 1990 PL B236 95 A New Experimental Limit on Neutron-Antineutron Transitions BERGER 1990 PL B240 237 Search for Neutron-Antineutron Oscillations in the FREJUS Detector BRESSI 1990 NC 103A 731 Final Results of a Search for Free Neutron Anti-Neutron Oscillations BRESSI 1989 ZPHY C43 175 Search for Free Neutron-Antineutron Oscillations TAKITA 1986 PR D34 902 Search for Neutron Antineutron Oscillation in ${}^{16}\mathrm {O}$ Nuclei FIDECARO 1985 PL 156B 122 Experimental Search for Neutron Antineutron Transitions with Free Neutrons PARK 1985B NP B252 261 Experimental Limits on Monopole Catalysis, ${{\mathit N}}{{\overline{\mathit N}}}$ Oscillations, and Nucleon Lifetime BATTISTONI 1984 PL 133B 454 Nucleon Stability, Magnetic Monopoles and Atmospheric Neutrinos in the Mont-Blanc Experiment JONES 1984 PRL 52 720 Search for ${{\mathit n}}{{\overline{\mathit n}}}$ Oscillation in Oxygen CHERRY 1983 PRL 50 1354 Experimental Test of Baryon Conservation: a New Limit on Neutron Antineutron Oscillations in Oxygen