Search for neutron-antineutron oscillations using multiprong events in Soudan 2

J. Chung, W. W.M. Allison, G. J. Alner, D. S. Ayres, W. L. Barrett, P. M. Border, J. H. Cobb, H. Courant, D. M. Demuth, T. H. Fields, H. R. Gallagher, M. C. Goodman, R. Gran, T. Joffe-Minor, T. Kafka, S. M.S. Kasahara, P. J. Litchfield, W. A. Mann, M. L. Marshak, R. H. MilburnW. H. Miller, L. Mualem, A. Napier, W. P. Oliver, G. F. Pearce, E. A. Peterson, D. A. Petyt, K. Ruddick, M. Sanchez, J. Schneps, A. Sousa, B. Speakman, J. L. Thron, S. P. Wakely, N. West

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65 Scopus citations


We have searched for neutron-antineutron oscillations using the 5.56 fiducial kiloton-year exposure of the Soudan 2 iron tracking calorimeter. We require candidate nn̄ occurrences to have ≥4 prongs (tracks and showers) and to have kinematics compatible with n̄N annihilation within a nucleus. We observe five candidate events, with an estimated background from atmospheric neutrino and cosmic ray induced events of 4.5±1.2 events. Previous experiments with smaller exposures observed no candidates, with estimated background rates similar to this experiment. We set a lifetime lower limit at 90% C.L. for the nn̄ oscillation time in iron: TA(Fe)>7. 2×1031 yr. The corresponding lower limit for oscillation of free neutrons is τnn̄-> 1.3×10 8 sec.

Original languageEnglish (US)
Article number032004
JournalPhysical Review D
Issue number3
StatePublished - 2002


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