15 - Gypsy

Summary

In November 1974, the elementary particle world was rocked by a surprising discovery. I was visiting Paris when the birth was announced of a new particle. ‘A new particle?’, you might wonder. ‘And there were so many already. What's the big deal?’ Well, it turned out to be a particle that did not fit into any of the existing series. Two groups of experimenters had made the discovery independently.

Samuel Ting was leading an experiment in Brookhaven, near New York, in which very high energy protons were made to collide with a target made of heavier material. Over several months, he and his collaborators had been observing a curious ‘signal’ in their apparatus. Ting found it difficult to believe that this signal was to be identified as a new particle, because, if this were true, it had to be something really spectacular. He went off to check and double check (including the possibility that he was the victim of some practical joke), and he ordered complete secrecy from all his collaborators.

The new particle, which he called J, would decay extraordinarily efficiently into an electron and a positron. It was these two particles that Ting detected in pairs, and when he measured their relative energies, it was found that they apparently originated from a new chunk of material with a mass of 3100 MeV (more than three times the proton mass).