Experimental Test of Baryon Conservation: A New Limit on the Nucleon Lifetime

The result of a search for nucleon decay using a 300-ton water Čerenkov detector located in the Homestake gold mine is reported. The nucleon total lifetime is found to be T_N>3×10³¹B_μ yr, where B_μ is the model-dependent probability for production and detection of a decaying muon following a nucleon decay event. In the SU(5) grand unified model, published calculations of B_μ vary from 5% to 10%, thereby yielding nucleon total lifetime limits in the range (1.5-3)×10³⁰ yr.