The Homestake Tracking Spectrometer a One-Mile Deep 1400-Ton Liquid Scintillation Nucleon Decay Detector

Abstract

We describe a proposed nucleon decay detector able to demonstrate the existence of nucleon decay for lifetimes up to 5 × 10³² yr. The proposed instrument is a self-vetoed completely-active 1400-ton liquid scintillation Tracking Spectrometer to be located in the Homestake Mine at a depth of 4200 mwe, where the cosmic ray muon flux is only 1100/m² /yr, more than 10⁷ times lower than the flux at the earth’s surface. Based on computer simulations and laboratory measurements, the Tracking Spectrometer will have a spatial resolution of ± 15 cm (0.32 radiation lengths); energy resolution of ± 4.2%; and time resolution of ± 1.3 ns. Because liquid scintillator responds to total ionization energy, all neutrinoless nucleon decay modes will produce a sharp (± 4.2%) total energy peak at approximately 938 MeV, thereby allowing clear separation of nucleon decay events from atmospheric neutrino and other backgrounds. The instrument will be about equally sensitive to most nucleon decay modes. It will be able to identify most of the likely decay modes (including $n \to \nu + \rm{k}_s^o$ as suggested by supersymmetric grand unified theories¹), as well as determine the charge of lepton secondaries and the polarization of secondary muons.

Work supported in part by the U.S. Dept. of Energy under contract DE-AC02-81-ER-40012 and in part by the U.S. National Science Foundation under grant AST-79-08670.