a Search for Nucleon Decay with Multiple Muon Decays

A search was made for nucleon decays which result in multiple delayed muon decays using the HPW (Harvard -Purdue-Wisconsin) water Cerenkov detector. The HPW detector consists of 680 metric tons of purified water instrumented with 704 five-inch photomultiplier tubes. The phototubes are situated on a volume array with a lattice spacing of approximately one meter, and the inside walls of the detector are lined with mirrors. This combination of mirrors and a volume array of phototubes gives the HPW detector a low trigger energy threshold and a high muon decay detection efficiency. The detector is surrounded by wire chambers to provide an active shield, and is located at a depth of 1500 meters-of-water-equivalent in the Silver King Mine in Park City, Utah. The entire HPW data set, consisting of 17.2 million events collec- ted during 282 live days between May 1983 and October 1984, was analyzed. No contained events with multiple muon decays were found in a 180 ton fiducial volume. This is consistent with the background rate from neutrino interactions, which is expected to be 0.7 (+OR-) 0.2 events. The calculated lower lifetime limit for the decay mode p (--->) (mu)('+)(mu)('+)(mu)('-) is: (tau)/B.R. = 1 x 10('31) years (90% C.L.). Limits are calculated for ten other proton decay modes and five bound neutron decay modes, most of which are around 4 x 10('30) years (90% C.L.). No previous studies have reported results from direct searches for eight of these modes.