Fermi’s description of the weak force was incomplete. According to his theory the probability for a reaction at very high energies could exceed 1, which is impossible. It was therefore important to study the weak force at high energies, but the problem was how! It was possible to produce beams of particles with high energy, but these particles either interacted electromagnetically or strongly. As both the electromagnetic and the strong force dominate over the weak force the latter will not be noticeable in the competition. It was in November 1959 after a discussion during coffee-break at Colombia University that Melvin Schwartz got the idea:

One should use neutrinos!

The neutrinos would come from the decays of pi-mesons. The question was whether neutrinos produced together with muons could give rise to both electrons and muons or exclusively muons.

The hunt for the muon neutrino had started!