Are protons for ever

Attempts by theoretical physicists to unite electromagnetic, weak and strong interactions into a single framework have raised the question about the validity of the law of number conservation according to which proton is stable. However, unification schemes put forward imply that at very high energies, equivalent to about 1015 times that of proton mass, quarks, which are the building blocks of baryons, can change into leptons leading to the decay of protons and bound neutrons. Theoretical predictions according to these schemes indicate that the life-time of proton could be between 1029 and 1033 years. Massive detector systems have been planned at various places in the world and put into operation to scrutinise experimentally the proton decay events. These are described in brief and the system set up at the Kolar Gold Field (KGF) is described in detail. During the first 10 months of operation of the KGF experiment, 3 events out of the recorded events suggest nucleon decay, but still do not qualify for an unambiguous proof of nucleon decay. (K.M.)