Search for nucleon decay into lepton+K{sup 0} final states using Soudan 2

A search for nucleon decay into two-body final states containing K{sup 0} mesons has been conducted using the 963 metric ton Soudan 2 iron tracking calorimeter. The topologies, ionizations, and kinematics of contained events recorded in a 5.52 kiloton-year total exposure (4.41 kton-year fiducial volume exposure) are examined for compatibility with nucleon decays in an iron medium. For proton decay into the fully visible final states {mu}{sup +}K{sub S}{sup 0} and e{sup +}K{sub S}{sup 0}, zero and one event candidates are observed respectively. The lifetime lower limits ({tau}/B) thus implied are 1.5x10{sup 32} yr and 1.2x10{sup 32} yr, respectively. Lifetime lower limits are also reported for proton decay into l{sup +}K{sub l}{sup 0}, and for neutron decay into {nu}K{sub S}{sup 0}. (c) 2000 The American Physical Society.