Particle and astrophysical results from underground experiments

Underground physics experiments have emerged in the last five years as unique tools to study a wide variety of problems in physics and astrophysics. The scale and location of these experiments was initially motivated by a search for proton decay. From prior experiments, the proton was known to live at least 1029 years. A number of theories suggest a value for the lifetime in the range of 1030 years. To study such lifetimes in a reasonable period requires detectors in the range of 1000 metric tons. In conducting such a sensitive experiment, one must take great care in shielding the detector from spurious signals. To eliminate the hadronic and electromagnetic component of cosmic rays, proton decay detectors are located deep underground. The surviving components of cosmic rays are very energetic muons that penetrate from the surface, along with neutrinos formed by cosmic ray interactions in the atmosphere that propagate unattenuated through the earth. The neutrinos form the ultimate background to proton decay. One of the major tasks of proton decay experiments is to make neutrino background estimates that are consistent with known physics and the behavior of their detector. In addition, as the authors see in the fourth section below, the environment required for proton decay experiments is ideal for a large number of other physics objects