Search for the proton decay mode p → ν K+ in Soudan 2

Abstract We have searched for the proton decay mode p → ν K + using the one-kiloton Soudan 2 high resolution calorimeter. Contained events obtained from a 3.56 kiloton-year fiducial exposure through June 1997 are examined for occurrence of a visible K + track which decays at rest into μ + ν or π + π 0 . We found one candidate event consistent with background, yielding a limit, τ/B(p → ν K + )>4.3×10 31 years at 90% CL with no background subtraction.