Searches for Proton Decay and Superheavy Magnetic Monopoles

In conclusion, as of 1984 January, it may be stated that the existence of super-heavy monopoles and the phenomenon of nucleon decay, both of which are extremely important from the point of view of grand unification theories, are still very open questions. While there has been just one magnetic monopole candidate so far, there have been several as far as nucleon decay is concerned. The first candidates for nucleon decay came from the fine-grain calorimeters of KGF, and NUSEX; recently there have been candidates from the water Cerenkov experiments as well. The experimental situation regarding the other important phenomena of relevance to grand unification which we have not discussed in this article — like the finite mass of neutrinos, neutrino oscillations, and neutron oscillations — continues to be indefinite though many dedicated experiments are in progress. With the continued operation of the nucleon decay experiments already collecting data and the commissioning of the new generation of experiments over the next few years, the stage is set for a resolution of this problem in a time scale of 5–10 years. The present indication that the dominant decay mode for the proton (even if it decays) is notp → e⁺π⁰ and that the lower limit to the lifetime of the nucleon is 10³¹ yr, does not favour the simple SU(5) type models. The remarkable discoveries of W^± and Z⁰ with mass values exactly as predicted, have given a boost to the unification based on the gauge theoretical approaches. Whether grand unification can be extended to super-unification, experiment alone can tell. This will be the challenge for the remaining years of this century.