Search for the Proton Decay Mode proton to neutrino K+ in Soudan 2

TL;DR

This study searched for proton decay into a neutrino and K+ using the Soudan 2 detector, setting new limits on the proton's lifetime with no confirmed decay events observed.

Contribution

First search for the proton to neutrino K+ decay mode using Soudan 2, establishing a new lower limit on proton lifetime at 90% confidence level.

Findings

No definitive proton decay events observed.

Set a lower limit on proton lifetime: tau/B > 4.3 x 10^{31} years.

One candidate event consistent with background.

Abstract

We have searched for the proton decay mode proton to neutrino 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 mu+ nu or pi+ pi0. We found one candidate event consistent with background, yielding a limit, tau/B > 4.3 10^{31} years at 90% CL with no background subtraction.