When physicists at the Fermi National Laboratory in the U.S. observed traces of the top quark -- the remaining undetected member of this most important family of fundamental particles -- this sent waves of excitement throughout the scientific community. News of this discovery, widely covered in the media climaxed an over three-decade-long study of quarks -- the building blocks of matter governed by the strong nuclear force, namely, most of the visible material universe.
Unknown to many outside the field is the fact that one of the first physicists to suggest the existence of top quark and the one who gave it its name is Weizmann Institute President Prof. Haim Harari. In a 1975 paper in Physics Letters, Prof. Harari postulated that apart from the three species of quarks that had already been observed and a fourth one which was just discovered there was a theoretical "need" for two additional heavy quarks with charges of 2/3 and -1/3. He named the two new proposed quarks "top" and "bottom," names that remain in use today.
The original model, presented then by Harari, needed major modifications, but a few months later in his rapporteur lecture at the year's International Conference on particle physics, Harari presented for the first time the full correct picture of the world of quarks and leptons, as we know it today, consisting of six species of quarks and six species of leptons. That picture has become the standard understanding. It was followed by the discovery of the bottom quark in 1977.
Commenting on the new Fermilab data, Harari says that while seeing traces of the top quark was of major importance, physicists were convinced of its existence for the last 19 years. But because the top quark has the largest mass of all quarks, experimental evidence about it could only be gathered with accelerators operating at the cutting edge of high-energy technology, a situation that delayed its detection.
Elementary particle physics has matured considerably since 1975, and it is now known that the experiments around which Harari built his early theory were not correctly interpreted. Nevertheless, subsequently gathered data have provided a firm basis for the presently accepted Standard Model of the material universe, which assumes -- as Harari did -- a six-member family of quarks.
This work, says Harari, is still far from complete. For one, the measurement of the top quark at Fermilab still needs further conformational studies. In addition, the theoretical relationship between the quarks and the second central family of particles, the leptons, still has to be ironed out, several different approaches having already been formulated. Whatever future developments will be, the excitement surrounding particle physics shows no signs of dying down.
Prof. Harari occupies the Annenberg Chair of High Energy Physics.