GUT monopole detection with scintillator

Searches for the monopoles predicted by Grand Unified Theories (GUTs) have required new approaches, since these monopoles should be both slow and highly penetrating. The ability of scintillator to respond to particles of velocity < 10^(-3) c has been demonstrated, indicating that scintillator detectors should be useful in GUT monopole searches. A small monopole detector prototype at the Earth's surface was operated in an effort to understand the problems and possibilities of monopole detection. The design philosophy, techniques, and the lessons learned from the prototype detector could then be applied to much larger monopole detectors. The prototype was not able to set new limits for the GUT monopole flux in cosmic rays, but in a more general analysis it was found that new limits could be set on the flux of lightly ionizing particles of mass ~ 10^(10) GeV. When GUT monopole detectors are scaled up to the size needed to challenge astrophysical limits, it becomes more likely that a flux could be found. This motivates a more careful examination of the scintillator counters, since their signal should be clear and unambiguous for a monopole candidate. The performance of the liquid scintillator counters for the MACRO (Monopole And Cosmic Ray Observatory) experiment was given considerable scrutiny, both to try to understand the observed behavior of these counters, and also to improve them for monopole detection. The results of these tests indicate that MACRO should be able either to establish a monopole flux or to limit it to a small fraction of the 'missing mass' of the universe.