Search for Nucleon Decay with Final States l+ eta, nubar eta, and nubar pi+,0 Using Soudan 2

TL;DR

This study searched for specific nucleon decay modes using the Soudan 2 detector, setting new lower limits on their lifetimes based on observed events and non-observations.

Contribution

First search for nucleon decay into five two-body final states with Soudan 2, establishing new lifetime lower bounds for these decay modes.

Findings

Zero events for proton decay into mu+ eta.

One event for proton decay into e+ eta.

Lifetime lower limits up to 89 x 10^30 years.

Abstract

We have searched for nucleon decay into five two-body final states using a 4.4 kiloton-year fiducial exposure of the Soudan 2 iron tracking calorimeter. For proton decay into the fully visible final states mu+ eta and e+ eta, we observe zero and one event, respectively, that satisfy our search criteria for nucleon decay. The lifetime lower limits (tau/B) thus implied are 89 x 10^30 years and 81 x 10^30 years at 90% confidence level. For neutron decay into nubar eta, we obtain the lifetime lower limit 71 x 10^30 years. Limits are also reported for neutron decay into nubar pi0, and for proton decay into nubar pi+.