Search for nucleon decay into lepton + K0 final states using Soudan 2

Abstract

A search for nucleon decay into two-body final states containing K^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^+K^0_s and e^+K^0_s, zero and one event candidates are observed respectively. The lifetime lower limits (\tau /B) thus implied are 1.5 \times 10^{32} years and 1.2 \times 10^{32} years, respectively. Lifetime lower limits are also reported for proton decay into l^+K^0_l, and for neutron decay into \nu K^0_s.