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 (+23 others)
2002 Physical Review D, Particles and fields  
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 n-nbar occurrences to have .GE. 4 prongs (tracks and showers) and to have kinematics compatible with nbar-N 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
more » ... osures observed no candidates, with estimated background rates similar to this experiment. We set a lifetime lower limit for oscillation time in iron: T_A(Fe) > 7.2x10^31 years. The corresponding lower limit for oscillation of free neutrons is τ_n-nbar > 1.3x10^8 seconds.
doi:10.1103/physrevd.66.032004 fatcat:uz37d3uxffemji556jmfl7fx3m